River channel width controls blocking by slow-moving landslides in California's Franciscan mélange

Finnegan, Noah J.; Broudy, Kiara N.; Nereson, Alexander L.; Roering, Joshua J.; Handwerger, Alexander L.; Bennett, Georgina

doi:https://doi.org/10.5194/esurf-7-879-2019

Articles | Volume 7, issue 3

https://doi.org/10.5194/esurf-7-879-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/esurf-7-879-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 7, issue 3

Research article

|

20 Sep 2019

Research article |

| 20 Sep 2019

River channel width controls blocking by slow-moving landslides in California's Franciscan mélange

Noah J. Finnegan, Kiara N. Broudy, Alexander L. Nereson, Joshua J. Roering, Alexander L. Handwerger, and Georgina Bennett

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Final revised paper (published on 20 Sep 2019)
Preprint (discussion started on 18 Oct 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of “Fluvial boulder transport controls valley blocking by earthflows in the California Coast Range, USA.”', Jeffrey P Prancevic, 05 Dec 2018
RC2: 'Review: Fluvial boulder transport controls valley blocking by earthflows in the California Coast Range, USA', Anonymous Referee #2, 02 Jan 2019
AC1: 'Reviewer Response', Noah Finnegan, 07 May 2019

Peer-review completion

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

AR by Anna Wenzel on behalf of the Authors (23 May 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 May 2019) by Paola Passalacqua

RR by Jeffrey P Prancevic (15 Jun 2019)

Suggestions for revision or reasons for rejection

I again enjoyed reading the revised version of this manuscript. The authors did an excellent job of addressing the previous set of reviewer comments, and I find the revised story to be much more compelling. I have only one (very) small remaining concern about the interpretation of the evidence presented in the manuscript, and that can likely be easily addressed. My concern is that the authors use earthflow flux as a direct measurement of boulder supply rate, when comparing the boulder supply rates of the two earthflows (Boulder Creek and Oak Ridge). However, this assumes that the two earthflows contain the same fraction of boulders. Isn't it possible that one earthflow contains 10% boulders, while the other contains 50% boulders? This assumption should be stated explicitly in the analysis, perhaps with some anecdotal justification from the authors' experience walking around these two landscapes. Other than that, I have just a few suggestions that require no response.

Line comments (no response required):
line 7.9. missing period

lines 8.15 - 17. Why not show the bankfull flow depth on Figs. 5C, 6C, and 7C?

Sec. 3.2. But this does not mean that the boulder concentration is the same, because we don't know the what proportion of the earthflow material is boulders for either earthflow. They could potentially be very different. Perhaps you could draw on your collective field observations to make the case that boulder fractions are similar between to the two sites?

line 9.29. Is "Highway 201" supposed to be "Mile 201?"

lines 10.30 - 31. How did time fall out of the units for the fluxes? Should be m^2/yr?

lines 10.34 - 35. I agree that this is probably the case, but it's not clear that boulder supply rates per unit channel width are the same between the two sites just because earthflow fluxes are the same between the two sites. See comment above on Sec. 3.2.

line 13.7 Missing space "2016)generally"

Fig. 7. Does this figure look way too busy if the earthflow reaches are shaded in red, similar to Figs. 5 and 6?

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RR by Isaac Larsen (02 Jul 2019)

ED: Publish subject to minor revisions (review by editor) (18 Jul 2019) by Paola Passalacqua

AR by Anna Mirena Feist-Polner on behalf of the Authors (29 Jul 2019) Author's response

ED: Publish as is (09 Aug 2019) by Paola Passalacqua

ED: Publish as is (12 Aug 2019) by Tom Coulthard(Editor)

Short summary

In some settings, landslides trigger valley blockages that impound huge volumes of sediment, often drastically changing river habitat and habitability. In other settings, landslides appear to have little effect on rivers. In this study, we explore what governs the different sensitivity of rivers to blocking from landslide debris. We accomplish this by comparing two sites in California with dramatic differences in blocking from otherwise similar slow-moving landslides.