the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Feb 2021
Evolution of the Tazones Lighthouse slope (Cantabrian coast, N Spain). Multidisciplinary monitoring between 2018 and 2020
Abstract. The Tazones Lighthouse slope shows different active mass movements affecting an area of 70.000 m2 of the Cantabrian Coast (N Spain), characterized by almost vertical rocky cliffs developed on Jurassic rocks: alternating marl, sandstone and limestone with three main stratigraphic and structural discontinuity families. Between June 2018 and May 2020, 22 monthly monitoring campaigns have been carried out to measure the displacement of 38 control points, located between 95–110 masl. The total station monitoring has been complemented by ortophoto analysis and detailed digital terrain models (DTM) from two drone flights. Since the beginning of the 3D monitoring, about the 50 % of the markers moved more than 1 m, one of them exceeding 15 m. Detailed DTM has shown that the increased activity is controlled by the discontinuities. There is an extraordinary correlation between displacement acceleration and precipitation and soil moisture: the largest displacements have occurred after 2 periods of intense rain (January and October–November 2019, with a maximum 24-hour precipitation of 64.5 mm and 82.1 mm, respectively, and soil moisture values higher than 90 %). This represents an exceptional opportunity to analyse in real time the Jurassic cliffs retreat of the Cantabrian Coast, a question that remained not quantified.
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RC1: 'Comment on nhess-2021-16', Alan Trenhaile, 21 Feb 2021
This is an interesting paper which is most notable perhaps for the frequent (monthly) monitoring of slope movement, and associated opening of fissures, on top of a cliff in northern Spain. It will make a useful contribution to the coastal literature once some changes have been made, the most important of which is to the English, which at present is rather poor. I have used the abstract in an attached copy of the manuscript to provide an example of the amount of work that needs to be undertaken on this aspect of the manuscript, but given the problem is throughout the paper I have limited most grammatical comments to only this section. I am also opposed to the results and discussion being combined in a paper. The results simply provide data, statistical analysis, and other qualititative or quantitative findings from a research project, whereas the discussion is used to discuss interpretations, implications, models, etc derived from the results. I find the Results and Discussion section to be poorly organised. Some of it belongs in the study area section and others in a Discussion rather than results section. I would begin this section with the displacement data from which everything else follows (interpretations, relationships with geology etc).
I also wonder about the assumption that mass movements in this area are generally fairly small. Surely, despite the lack of historical records at this particular site, the rapid opening up of some of the fissures must lead to a large slope failure. Depending on the depth of the failure surface this may only involve shearing of material from the upper part of the cliff but even this, given minimum depths and the distance of the fissures from the cliff edge, would involve a huge amount of material. I would like to see more discussion of this possibility and also an explanation of why there has been such a dramatic increase in the width of some fissures in the last few years.
There is also an implication in places in this paper that mass movement is the main mechanism rather than marine processes. Steep sea cliffs occur along coasts for one reason, which is oversteeping and resulting instability due to marine (usually waves in temperate regions). Without marine processes there would be no steep cliff and no mass movement. Precipitation may trigger mass movements (that is determine when they occur) but the conditions for their occurrence is determined by the sea. Incidentally, the present dominance of blocks on the beach (relative to pebbles) is not evidence of mass movement dominance. If mass movement blocks were dominant here it would prevent marine erosion of an increasingly buried cliff foot. The cliff would then be essentially abandoned by the sea and would gradually become less steeply sloping and more vegetated. This is not happening - this is an active sea cliff with a steepness and internal geology that promotes a certain suite of mass movements.
I suspect you are quite right to relate mass movements to precipitation etc but there is also a possibility that wave activity may at least play a role, given that winter storms are also times when waves are highest. This can lead to enhanced undercutting and instability as well as generating vibrations in the cliff materials (eg. Thompson, C.F., Young, A.P., Dickson, M.E., 2019. Wave impacts on coastal cliffs: Do bigger waves drive greater ground motion? Earth Surface Processes and Landforms, 44, 2849-2860. and Earlie, C., Masselink, G., Russell, P., 2018. The role of beach morphology on coastal cliff erosion under extreme waves. Earth Surface Processes and Landforms, 43, pp.1213-1228).
The last point in the introduction claims that this research will "provide a solid knowledge base to perform predictive models of coastal retreat in future scenarios". Will it ? In truth while I consider this paper to be a useful addition to the literature, there really isn't anything fundamentally new about the results (no new theory or model, etc). How then do you think it can help us to develop predictive models ? Surely much of what is presented in this and many similar papers is site specific - strongly related to conditions at the study area. Please justify your statement in the conclusions.
Other comments and suggestions are listed in the attached annotated version.
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AC1: 'Reply on RC1', María José Domínguez-Cuesta, 09 Mar 2021
Dear Dr. Alan Trenhaile,
We are very grateful for your review of our manuscript. Thank you very much for your constructive comments and suggestions. We consider that they will contribute to improve our manuscript and we really appreciate your effort.
In the new version of the manuscript, we will incorporate all your observations.
Sincerely
Citation: https://doi.org/10.5194/nhess-2021-16-AC1 -
AC3: 'Reply on RC1', María José Domínguez-Cuesta, 05 Apr 2021
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-16/nhess-2021-16-AC3-supplement.pdf
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AC1: 'Reply on RC1', María José Domínguez-Cuesta, 09 Mar 2021
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RC2: 'Comment on nhess-2021-16', Anonymous Referee #2, 08 Mar 2021
I was greatly looking forward to reviewing this paper being a subject of interest and some experience to me. However, the paper is very limited in scope and has a number of failings which fall short of the standard to be published in the journal:
- Limited scientific data is presented, basically several years of surface movement data, some rainfall analysis, and three joint measurements. Consequently there is insufficient site investigation to support the narrative which is somewaht speculative and confused in places. Even some of this limited data is poorly presented e.g. the joint data plotted on a steroenet is not provided.
- The site is compared to Holderness UK which is unfortunate because this does not provide a comparative analogue to support the observations at Tazones. The two sites are formed in very different geologies, the former Quaternary soft sediments subject to high rates of cliff toe erosion and episodic rotational failures. The latter being formed in Jurassic rocks that appear controlled by bedding and structural discontinuities.
- The authors present a short snap shot in time in the development of the landslide for which there is evidence of pre-failure as far back as 1984. The evolutionary setting in space and time is fundamental to understanding the causes, mechanisms and behaviour of the landslide; the authors have not done this. They could have produced a detailed geomorphological map of the coastal slopes and foreshore to set the landslide in context with the surroundings. They make no mention of the foreshore and the potential changes and contribution of erosion in the landslide development. What influence has the nearby groyne played in the exposure of the cliffs to high energy waves I wonder.
- Some considerable assumptions are made without site validation i.e. no ground investigation or testing of soils has been carried out or presented. This would be an expectation for a landslide investigation.
- The authors are confused about the landslide mechanism and reference to Holderness. It may have helped if they had referenced international landslides classifications such as Varnes 1988; Dikau and Brunsden 1996. Also, reference to other literature on Jurassic coast landslides e.g. Lyme Regis, UK. The dominant control is the sub-horizontal bedding which forms basal shear surfaces. The vertical cracks and joints form detachment surfaces. The discussion and narrative is rather speculative and not supported by evidence with the exception of the movement and rainfall records.
- The conclusion that the landslide will evolve "without involving large volumes of material in a single episode" is simply wrong from the photo evidence, which clearly indicates potential for deep-seated landslides, which are episodic in time.
- The strength of the paper is the relationship between rainfall and ground movement. What is presented is consistent with other well investigated deep landslide sites e.g. Moore 2020 Undercliff, Isle of Wight. But the issue is this is a short snapshot in time and in no way can be used to corroborate the evolution of the site over longer time scales, in this case up to 3 decades.
- Finally, the standard of English would need to be improved for publication. The structure should also be improved, better introduction and reference to appropriate literature op.cit., expand the approach to set the site in context (geomorphology!); presentation of results section, discussion and conclusions. As it stands, the paper falls short of achieving this.
-
AC2: 'Reply on RC2', María José Domínguez-Cuesta, 09 Mar 2021
We thank Anonymous Referee #2 for his/her revision. We really appreciate the comments and suggestions. We will include the suggested amendments in our point-by-point response on which we are currently working. In the revised version of the manuscript, we will try to clarify and explain in detail those parts that raise doubts to avoid misunderstandings.
Citation: https://doi.org/10.5194/nhess-2021-16-AC2 -
AC4: 'Reply on RC2', María José Domínguez-Cuesta, 05 Apr 2021
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-16/nhess-2021-16-AC4-supplement.pdf
Status: closed
-
RC1: 'Comment on nhess-2021-16', Alan Trenhaile, 21 Feb 2021
This is an interesting paper which is most notable perhaps for the frequent (monthly) monitoring of slope movement, and associated opening of fissures, on top of a cliff in northern Spain. It will make a useful contribution to the coastal literature once some changes have been made, the most important of which is to the English, which at present is rather poor. I have used the abstract in an attached copy of the manuscript to provide an example of the amount of work that needs to be undertaken on this aspect of the manuscript, but given the problem is throughout the paper I have limited most grammatical comments to only this section. I am also opposed to the results and discussion being combined in a paper. The results simply provide data, statistical analysis, and other qualititative or quantitative findings from a research project, whereas the discussion is used to discuss interpretations, implications, models, etc derived from the results. I find the Results and Discussion section to be poorly organised. Some of it belongs in the study area section and others in a Discussion rather than results section. I would begin this section with the displacement data from which everything else follows (interpretations, relationships with geology etc).
I also wonder about the assumption that mass movements in this area are generally fairly small. Surely, despite the lack of historical records at this particular site, the rapid opening up of some of the fissures must lead to a large slope failure. Depending on the depth of the failure surface this may only involve shearing of material from the upper part of the cliff but even this, given minimum depths and the distance of the fissures from the cliff edge, would involve a huge amount of material. I would like to see more discussion of this possibility and also an explanation of why there has been such a dramatic increase in the width of some fissures in the last few years.
There is also an implication in places in this paper that mass movement is the main mechanism rather than marine processes. Steep sea cliffs occur along coasts for one reason, which is oversteeping and resulting instability due to marine (usually waves in temperate regions). Without marine processes there would be no steep cliff and no mass movement. Precipitation may trigger mass movements (that is determine when they occur) but the conditions for their occurrence is determined by the sea. Incidentally, the present dominance of blocks on the beach (relative to pebbles) is not evidence of mass movement dominance. If mass movement blocks were dominant here it would prevent marine erosion of an increasingly buried cliff foot. The cliff would then be essentially abandoned by the sea and would gradually become less steeply sloping and more vegetated. This is not happening - this is an active sea cliff with a steepness and internal geology that promotes a certain suite of mass movements.
I suspect you are quite right to relate mass movements to precipitation etc but there is also a possibility that wave activity may at least play a role, given that winter storms are also times when waves are highest. This can lead to enhanced undercutting and instability as well as generating vibrations in the cliff materials (eg. Thompson, C.F., Young, A.P., Dickson, M.E., 2019. Wave impacts on coastal cliffs: Do bigger waves drive greater ground motion? Earth Surface Processes and Landforms, 44, 2849-2860. and Earlie, C., Masselink, G., Russell, P., 2018. The role of beach morphology on coastal cliff erosion under extreme waves. Earth Surface Processes and Landforms, 43, pp.1213-1228).
The last point in the introduction claims that this research will "provide a solid knowledge base to perform predictive models of coastal retreat in future scenarios". Will it ? In truth while I consider this paper to be a useful addition to the literature, there really isn't anything fundamentally new about the results (no new theory or model, etc). How then do you think it can help us to develop predictive models ? Surely much of what is presented in this and many similar papers is site specific - strongly related to conditions at the study area. Please justify your statement in the conclusions.
Other comments and suggestions are listed in the attached annotated version.
-
AC1: 'Reply on RC1', María José Domínguez-Cuesta, 09 Mar 2021
Dear Dr. Alan Trenhaile,
We are very grateful for your review of our manuscript. Thank you very much for your constructive comments and suggestions. We consider that they will contribute to improve our manuscript and we really appreciate your effort.
In the new version of the manuscript, we will incorporate all your observations.
Sincerely
Citation: https://doi.org/10.5194/nhess-2021-16-AC1 -
AC3: 'Reply on RC1', María José Domínguez-Cuesta, 05 Apr 2021
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-16/nhess-2021-16-AC3-supplement.pdf
-
AC1: 'Reply on RC1', María José Domínguez-Cuesta, 09 Mar 2021
-
RC2: 'Comment on nhess-2021-16', Anonymous Referee #2, 08 Mar 2021
I was greatly looking forward to reviewing this paper being a subject of interest and some experience to me. However, the paper is very limited in scope and has a number of failings which fall short of the standard to be published in the journal:
- Limited scientific data is presented, basically several years of surface movement data, some rainfall analysis, and three joint measurements. Consequently there is insufficient site investigation to support the narrative which is somewaht speculative and confused in places. Even some of this limited data is poorly presented e.g. the joint data plotted on a steroenet is not provided.
- The site is compared to Holderness UK which is unfortunate because this does not provide a comparative analogue to support the observations at Tazones. The two sites are formed in very different geologies, the former Quaternary soft sediments subject to high rates of cliff toe erosion and episodic rotational failures. The latter being formed in Jurassic rocks that appear controlled by bedding and structural discontinuities.
- The authors present a short snap shot in time in the development of the landslide for which there is evidence of pre-failure as far back as 1984. The evolutionary setting in space and time is fundamental to understanding the causes, mechanisms and behaviour of the landslide; the authors have not done this. They could have produced a detailed geomorphological map of the coastal slopes and foreshore to set the landslide in context with the surroundings. They make no mention of the foreshore and the potential changes and contribution of erosion in the landslide development. What influence has the nearby groyne played in the exposure of the cliffs to high energy waves I wonder.
- Some considerable assumptions are made without site validation i.e. no ground investigation or testing of soils has been carried out or presented. This would be an expectation for a landslide investigation.
- The authors are confused about the landslide mechanism and reference to Holderness. It may have helped if they had referenced international landslides classifications such as Varnes 1988; Dikau and Brunsden 1996. Also, reference to other literature on Jurassic coast landslides e.g. Lyme Regis, UK. The dominant control is the sub-horizontal bedding which forms basal shear surfaces. The vertical cracks and joints form detachment surfaces. The discussion and narrative is rather speculative and not supported by evidence with the exception of the movement and rainfall records.
- The conclusion that the landslide will evolve "without involving large volumes of material in a single episode" is simply wrong from the photo evidence, which clearly indicates potential for deep-seated landslides, which are episodic in time.
- The strength of the paper is the relationship between rainfall and ground movement. What is presented is consistent with other well investigated deep landslide sites e.g. Moore 2020 Undercliff, Isle of Wight. But the issue is this is a short snapshot in time and in no way can be used to corroborate the evolution of the site over longer time scales, in this case up to 3 decades.
- Finally, the standard of English would need to be improved for publication. The structure should also be improved, better introduction and reference to appropriate literature op.cit., expand the approach to set the site in context (geomorphology!); presentation of results section, discussion and conclusions. As it stands, the paper falls short of achieving this.
-
AC2: 'Reply on RC2', María José Domínguez-Cuesta, 09 Mar 2021
We thank Anonymous Referee #2 for his/her revision. We really appreciate the comments and suggestions. We will include the suggested amendments in our point-by-point response on which we are currently working. In the revised version of the manuscript, we will try to clarify and explain in detail those parts that raise doubts to avoid misunderstandings.
Citation: https://doi.org/10.5194/nhess-2021-16-AC2 -
AC4: 'Reply on RC2', María José Domínguez-Cuesta, 05 Apr 2021
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-16/nhess-2021-16-AC4-supplement.pdf
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