Dear Leif, dear co-authors,

After reading carefully the reviews of all three parts, I have made my editorial decision.

There is clear consensus that the content and form of the three papers do not warrant three separate contributions.

My suggestion is thus that you merge the actual content into two papers. The first part should contain broadly the content of the actual contributions A and B, while the second part should, in my opinion, focus on the actual part C, expanded as we have discussed together. In this way, you can use the first part of the paper to present your data (very briefly, as most could go to Supplementary Information), then your methods to both derive cliffs and melt contributions, and your main results would focus on the melt contribution of both cliffs and debris-covered ice. You can then use the second paper to explain your results in the context of ice dynamics, surface features and focus on feedbacks. This second part should be strengthened (also as we discussed), and statements that resemble speculations (e.g. review of Anonymous referee 2 of Part C/1 of part B) should be backed up.

In particular, I suggest you add to the second contribution a new schematic figure that explains the ice cliff-ice dynamics-thinning feedback that we are trying to highlight, which was not described in a clear enough manner in the original paper/s.

Some of the content of actual part B can go into C.

This seems to me the best solution on how to present this very interesting work, which however in its current form (three contributions) comes across as repetitive and stretched and cannot be published without substantial revisions.

Please also address all the very good comments raised by all reviewers, and in particular those related to several aspects of your methods.

I am open for further specific discussion on which content should go where if this can help you, within the framework of this decision.

I hope you will agree. An alternative to this restructuring, also suggested by reviewers, would be to merge all content into one paper. This would be also acceptable for me, but I see the difficulties of condensing all the content into one paper.

I look forward to receiving your revised manuscript.

Francesca

Dear Leif and co-authors,

Thanks a lot for providing your revised manuscript, which is now a combination of part A and B of the original three parts submission, and has the potential to represent a solid contribution to the field that I am sure will be widely read once these final round of comments are included.

I have now received two very thorough and useful reviews, both of which indicate minor revisions but also list a number of comments that should all be addressed before the paper can be accepted for publication. Both reviewers point to the need to improve the presentation of your article, and the Discussion and Conclusions sections especially. The Supplementary Material also needs improvement, from formatting to style and avoiding repeating figures that are in the main paper.

I would also encourage you to carefully address reviewer 2 main point 2 on the underlying assumptions of your methods, and make them clear to the readers.

I notice that few of the comments in the previous round of reviews have not been addressed and would encourage you to do it now.

In summary, I ask that you to take into account all the reviewers points carefully. The manuscript in its present form is not acceptable for TC standard, and I'd like to thank both reviewers for investing a lot of their time to provide those many detailed suggestions. Importantly, in its current form the manuscript does not do justice to the large amount of interesting work that you and the co-authors put into this.

I do hope you will consider carefully all comments and make an effort to bring the manuscript to the standard it deserves. I am sure if you do this that this will be an important paper for the debris-covered glaciers community.

Looking forward to receiving your revised paper.

All the best,

Francesca

Dear Leif and co-authors,

Thank you for the revised paper, which I am happy to accept for publication after technical corrections. I am happy to see that you considered almost all issues raised – and that you addressed some of the more major ones raised by reviewer 2. I agree with your choice of how to treat the assumptions you made and the sensitivity/uncertainty analysis (mostly moved to the SI).

I have few technical details for you to address, as I feel the English of the text could still be more polished. I have suggested a restructured version of the abstract below, which maintains all your content of course. I feel the order of the paragraphs was not entirely logical, and some of the wording could be improved. Feel free to use that or a modified, more fluent and tidier version of yours. I would encourage the authors to go through their text once more, and try to polish it some more and correct style/grammar, based on some of my comments below (in few instances the text contains still grammar errors). This is something that the co-authors could help with.

Finally, I hope the authors are satisfied with this final paper version, which I feel is substantially improved. I also hope that they appreciate the constructive and very thorough reviews of their paper.

I look forward to see this paper published.
All the best,

Francesca

REVISED SUGGESTED ABSTRACT:
Many glaciers are thinning rapidly beneath melt-reducing debris cover, including the Kennicott Glacier in Alaska. The zone of maximum thinning at Kennicott Glacier is located under debris. Scattered within the debris cover, melt hotspots, such as ice cliffs, locally increase melt rates. We explore the roles of debris and ice cliffs in controlling rapid thinning under thick debris at Kennicott Glacier.
We collected abundant in situ measurements of debris thickness, sub-debris melt, and ice cliff backwasting allowing for extrapolation across the debris-covered tongue (the study area and the lower 24.2 km 2 of the 387 km 2 glacier). A newly developed automatic method, the Adaptive Binary Threshold, uses for the first time only optical satellite imagery to delineate ice cliffs. We show that the method accurately estimates ice cliff coverage even where ice cliffs are small and debris color varies.
Kennicott Glacier exhibits the highest fractional area of ice cliffs (11.7 %) documented to date. Ice cliffs contribute 26% of total melt across the glacier tongue. Although the relative importance of ice cliffs to area-average melt is significant, the absolute area-averaged melt is dominated by debris. At Kennicott Glacier, glacier-wide melt rates are not maximized in the zone of maximum thinning, and we show that this rapid thinning is due to a decline in ice discharge through time. There is more debris-covered ice in Alaska than any other region on Earth. Through our efforts, Kennicott Glacier is now the first in glacier in Alaska and the largest globally where melt across its debris-covered tongue has been rigorously quantified.

COMMENTS
COMMENTS RELATED TO THE REBUTTAL TEXT
_On line 265 of the document (in the authors’ reply to reviewer 1): you show as original and new paragraph exactly the same text! Please clarify here if and how you made changes to that text.
_Text on line 590: there is a “in” missing I assume?
Original text:
“Expanding and thickening debris cover should reduce glacier thinning relative to glaciers without debris (Banerjee, 2017; Gibson et al., 2017), but the melt-suppressing effect of debris is not always apparent the observed thinning patterns of glaciers even when debris is thick and debris coverage is extensive (e.g., Kaab et al., 2012; Gardelle et al., 2013)”.
It should be:
Expanding and thickening debris cover should reduce glacier thinning relative to glaciers without debris (Banerjee, 2017; Gibson et al., 2017), but the melt-suppressing effect of debris is not always apparent IN? the observed thinning patterns of glaciers even when debris is thick and debris coverage is extensive (e.g., Kaab et al., 2012; Gardelle et al., 2013)”.

_Lines 765 and following: In response to a comment by Reviewer 2: Krajeenbrink et al (2017) only consider ponds, not ice cliffs, in their melt estimates for HMA. I would also say that the evidence available until now suggests that the two do not melt at the same rate. So I suggest you rephrase the sentence you have added:
“While we do not explicitly document the melt rate of ponds and streams (i.e., melt hotspots) we follow Kraaijenbrink et al. (2017)’s approach and assume they melt at the same rate as ice cliffs. Using this logic, in order for ice cliffs (melt hotspots) in the ZMT to compensate for the insulating effects of debris, ice cliff (melt hotspot) area would need to increase from 11.7% to 90% of the glacier surface. Ice cliffs, ponds, and streams assuredly do not occupy 90% of the ZMT. This again suggests that ice cliff and other melt hotspots do not control the location of the ZMT.”

I would recommend that in this paragraph you simply state that you do not address ponds and streams here, that you will do it in a follow up publication, but that, given current estimates of their contributions to ablation, their inclusion will not change your main conclusions.
_Line 802: provide the source of that 20% value (your own digitisation).

_Line 876 and following: on uncertainty of ablation measurements: how do you combine the uncertainty in the marking and the uncertainty due to the tilt of the stake? Can you please explain?
_Line 946: the reviewer suggested added reference: “L231-2. Makes sense to reference (Steiner, Buri, Miles, Ragettli, & Pellicciotti, 2019) here”. And I would agree with that, even if this is one of our studies.
_Line 970: I agree with the reviewer that you should provide units.

COMMENTS RELATED TO THE REVISED TEXT
The following comments and lines refer to lines of the revised paper (in track-changes):
_Line 1340:
«Greater surface elevation changes»: say if these are positive of negatine, I assume you refer to thinning patterns here?
_Line 1434: I would remove this sentence
“leaving a detailed examination of other melt hotspots for another contribution.”, or rephrase it. The sentence has it is grants an explanation of why they are not included here, and does not add much to the paper. There will most likely be a second contribution, and readers will be aware of it.
_Line 1442
I would add, after (DEMs), “but showed that the method is sensitive to the DEMs resolution and its predictive skills diminish for coarser resolution”.

_Line 1448
Consider removing: “thereby addressing the questions outlined above»

_Line 1496: I would remove “better”

_Line 1566: I would rephrase as: We DEVELOP an automated algorithm to delineate ice cliffs from optical satellite imagery.

_Line 1567 and previous occurrences: WorldView (WV) satellite- check where you use WorldWiew as a word for the first time, provide the acronym there and be consistent in its use. You have used both acronym and extended word in the text before this occurrence.