Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake

Nagai, Hiroto; Watanabe, Manabu; Tomii, Naoya; Tadono, Takeo; Suzuki, Shinichi

doi:https://doi.org/10.5194/nhess-17-1907-2017

Articles | Volume 17, issue 11

https://doi.org/10.5194/nhess-17-1907-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/nhess-17-1907-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 11

Research article

|

13 Nov 2017

Research article |

| 13 Nov 2017

Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake

Hiroto Nagai, Manabu Watanabe, Naoya Tomii, Takeo Tadono, and Shinichi Suzuki

Download

Final revised paper (published on 13 Nov 2017)
Supplement to the final revised paper
Preprint (discussion started on 16 Sep 2016)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

- Printer-friendly version

- Supplement

RC1: 'Interactive comment on"Multiple remote sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha Earthquake" by Hiroto Nagai et al.', Anonymous Referee #1, 09 Oct 2016
- AC1: 'Answer to reviewer #1', Hiroto NAGAI, 24 Nov 2016
RC2: 'the use of remote sensing for the description of the catastrophic collapse occurred in Langtang Valley induced by 2015 Gorca Earthquake', Anonymous Referee #2, 23 Oct 2016
- AC2: 'Answer to reviewer #2', Hiroto NAGAI, 24 Nov 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by Editor and Referees) (26 Nov 2016) by Paolo Tarolli

AR by Hiroto Nagai on behalf of the Authors (06 Jan 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Jan 2017) by Paolo Tarolli

RR by Anonymous Referee #1 (23 Jan 2017)

RR by Anonymous Referee #2 (25 Jan 2017)

Suggestions for revision or reasons for rejection

The paper has been improved according to reviewers’ suggestions. In my opinion, the manuscript could be considered ready for the publication after minor revisions.
In the following a list of suggestions.
The paper describes well the management and processing of remote sensing data, but it is still poor from the geomorphological point of view. In particular, I suggest to describe better the event occurred starting from the abstract and then in the text.
For the abstract I suggest to describe better that (if I understood correctly) the work described the effect of the catastrophic avalanche deposit area. The paper analyzed the effects of different deposition processes that are the related to the catastrophic avalanche made by rock, ice and snow.
A good geomorphological description of the avalanche deposition area is missing in chapter 2 and a partial description of results from previous study, that considered also field surveys, are presented only at the end of the manuscript (chapter 4.2). I think that readers needs these details at the beginning of the text, to understand better what is occurred and what has been already published on this catastrophic event. At the end of the paper, in the discussion, authors can consider again bibliography to compare obtained results.
Another important element is figure 5a; this picture represents the area covered by avalanche deposits. This area has been divided in different sectors and (in my opinion) lectors should have the possibility to understand which choices did authors for dividing this area in sectors (morphological, sedimentological, thickness of deposits?). Again, the description from the geomorphological point of view is too poor to have a complete description of the event. This paper present a remote sensing application, but if authors want to work with natural disaster, they should provide a (complete) description of the case study also using elements and data already published.
Page 7 line 7: In this paragraph, authors described the volume change analysis. In particular, they assumed that negative changes are mistakes and they correct them to zero. In my experience, the transition zone of large landslides (and in particular of rock avalanches) is often characterized by negative changes that are caused by the erosional effect of the huge mass and its velocity. Of course I hadn’t the possibility to analyze “uncorrected” data, but I suggest that authors consider the possibility that this complex process can cause also negative changes during its runout.
The interpretation of DEM comparison results is often a very complex task. The recognition of real negative changes from artefacts can be usually based on the shape and distribution of negative areas. A morphological validation can be usually considered a good solution.
Considering language, I suggest to revise in particular the following paragraphs because they are not very clear:
Page 1, line 12 – 17: please consider to rewrite this paragraph because it is not very clear
Page 6, lines 14 and 15: sectors 1 to 4 are considered “dark” but also sectors 12 to 15 are considered dark too, is it correct?
Page 7, line 7 to 15: please consider to rewrite this paragraph because it is not very clear

Hide

ED: Reconsider after major revisions (further review by Editor and Referees) (01 Jun 2017) by Paolo Tarolli

AR by Hiroto Nagai on behalf of the Authors (14 Jul 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Jul 2017) by Paolo Tarolli

RR by Anonymous Referee #3 (31 Jul 2017)

Suggestions for revision or reasons for rejection

Title: Multiple remote sensing assessment of the catastrophic collapse in
Langtang Valley induced by the 2015 Gorkha Earthquake

Authors: Hiroto Nagai

General comments:

The paper presents the exploitation of multi-source Earth Observation data (radar and optical) for a detailed analysis of the avalanche event triggered by the 7.8 Gorkha earthquake. Radar images are used to rapidly identify the affected area. Optical images are used to map the landslide area and to interpret the deposition sequence. Then, using pre- and post-event DSMs, the landslide volume is assessed.
The paper well address a fundamental issue i.e., the need for a rapid assessment of landslide-affected area for urgent response in emergency situations.
The paper is of broad interest and surely suited for the journal scopes and themes. The paper is interesting and relevant for this journal and within its topics. Description of methodology is informative and data analysis is flawless.
In summary, the presented paper can represent, after some minor revisions (see below), a good addition to the literature.

Specific comments:

1) I appreciate the inclusion of the description of the avalanche event. I am sorry to notice that this description is poor and confusing. Please try to rephrase this part from general (description of the triggering event, including meteorological observation, and effects on wide area) to particular (description of the effects on the area of interest, dividing description of source area form accumulation zone);

2) Names of villages and rivers cited in the text should appear in the images for easy location;

3) I suggest to include borders of zones A to J in Figure 7A;

4) Discussion paragraph is still weak. Your work is valuable and of practical use, please discuss which area the advantages, disadvantages, limits, opportunities of your application.

Technical comments/Typing errors:
In general, in the reviewer’s opinion, the paper is not well-written. Some parts in the results and discussion paragraph are difficult to read fluently. Some sentences seem to be incomplete and confusing. Editing of English language and style is required. The reviewer is not an English native speaker. I would suggest a professional correction service.

Hide

RR by Anonymous Referee #2 (21 Aug 2017)

Suggestions for revision or reasons for rejection

The paper has been revised and improved following my suggestions. After the revision, some critical elements are still present in the manuscript.
In the following some suggestions:
Page 2 line 1: the first part of the introduction is good, but in the second page the topic change sharply. I suggest introducing and describing better the use of remote sensing data for damage detection: I also believe that many papers that described the characterization of large landslides using remote sensing dataset have been published in last years, and I think that these manuscripts should be cited in this second part of the introduction.
Page 2, chapter 2.2: some sentences are not very clear; I suggest a revision of the txt by an English native speaker.
Page 7 discussion: the organization of this chapter should be reconsider because there are both results and comments
From line 10 to line 27: these paragraph described some results obtained with SAR data, I believe that this part of the manuscript should be moved in the previous chapters.
From line 28 to (page 8) line 9: this second part is a real discussion.
Chapter 4.2 and 4.3: these paragraphs are a description of the validation and of the interpretation of the obtained results. I suggest authors to transfer these paragraphs in previous chapter. If authors disagree, I suggest that these paragraphs could remain inside chapter 4 but before the discussion of (page7) line 28 to (page 8) line 9. Chapter 4.3 represents reconstruction of sequence events and I think that it is one of the key point of the article. For this reason, I suggest that this reconstruction should published immediately after the description of the results.
After these changes, discussion and conclusion seem to be very short, I suggest to improve both.

Hide

ED: Publish subject to minor revisions (further review by Editor) (22 Aug 2017) by Paolo Tarolli

AR by Hiroto Nagai on behalf of the Authors (11 Sep 2017) Author's response Manuscript

ED: Publish as is (27 Sep 2017) by Paolo Tarolli

AR by Hiroto Nagai on behalf of the Authors (04 Oct 2017) Manuscript

Download

Article (18697 KB)
Full-text XML

Short summary

We demonstrated an assessment of the sediments caused by a catastrophic avalanche, induced by the main shock of the 2015 Gorkha Earthquake in Nepal. A Japanese space-borne sensor, PALSAR-2, have a high potential for delineating the hazardous zone. Comparison of pre- and post-high-resolution topographic data estimates the avalanche-induced sediment volume as 5.51 × 10⁶ m³. High-resolution satellite imagery revealed that it has multiple layers of sediment with different physical properties.