|This paper provides a useful review of the frequent surges of Harald Moltke Brae, and their strong seasonal variability. These velocity patterns haven’t been reported before, so the paper and the comprehensive data that it contains are a useful addition to the literature. I’m satisfied that the authors have addressed the substantive parts of my comments from the previous version.|
My comments below are generally minor in nature, and are mainly aimed at improving explanations and removing potential ambiguity in wording in a few places. I’m happy for the authors and editor to decide between them as to which of these will be addressed; I do not need to review the paper again.
L18-L23 & Fig. 1: I still find this first paragraph and figure strange as they dive straight into the results without providing any kind of methods or context for them. So I would still prefer to see them placed in the Results section where they properly belong, but from the author’s comments I can see that they disagree with my viewpoint. So I’m happy to leave the decision up to the editor as to whether anything should be changed here.
L24-32: as stated in my original review, this describes the Study Area and would be better placed later in the text. I believe that a more general overview of the topic of surging and its history at Harald Moltke Brae needs to be provided first, before getting into these specific details.
L31: change to ‘northern side of Harald Moltke Bræ at a centerline distance of about 20km’
L45: I think that ‘typically flows slower than the upper part’ would be a more accurate description
L80: I think that ‘always’ is unnecessary here and can be deleted
L81: ‘always 2 years’ would be better expressed as ‘both 2 years’
L95: would be useful to add a short explanation as to why monthly averaging is deemed to be appropriate here (e.g., to enable clear identification of seasonal velocity variations?)
L99: provide a brief explanation as to why the black triangle is chosen as the best place (indeed, only place) to plot the velocity time series. E.g., is this because it’s on the glacier centreline? near the terminus? undergoes the most dramatic velocity variations?
Table 1: will be useful if you can provide a URL for each of the data sources listed in the last row if one is available
L103: change to ‘by applying a method…’
L124: describe what kind of line you fit to the ice thickness profiles
L127-128: provide some more information about the CReSIS ground penetrating radar measurements. E.g., When were they measured? What’s their resolution? Where did you download the data from, and what’s the name of the dataset that you downloaded?
L131: provide a few more details about the RACMO data that you used: e.g., spatial resolution? where was it downloaded from?
L132-133: I find it a little difficult to follow the wording for the area over which your RACMO data is averaged. You specify that it’s a ‘fixed area’ and the ‘drainage area of a cross section which is located close to the glacier front at about 15km’, so do you mean that it’s the entire area of the glacier basin upglacier of the cross section at 15km? If so, then update the text to say this.
L134: provide some more detail as to how you computed the ice-mass flux through the cross section. E.g., did you assume that surface velocity was the same as depth-averaged velocity? Did you account for any change in ice thickness over time?
Figure 3 caption: change to ‘The documented surges are marked…’
Figure 4a & 6a: would be useful to add a dotted 0 line to part (a), so that it’s clearer as to which years are positive and negative SMB
Figure 4 & 6: if there is sufficient space, I wonder if these two figures could be merged into a single continuous timeline? This would make it easier to see how the surges compare to each other. But if this will end up with data points being too small to clearly see, then no problem to leave them as separate figures.
Figure 5c and 5d and others (e.g., Fig. 7, 9): specify in the x-axis label or the caption that distance is from the 1916 terminus, and indicate where the current terminus is (i.e., similar to how the terminus is labelled in Fig. 13b)
L176: change to ‘one order of magnitude’
Figure 12: add shading to this figure to indicate the timing of the surge events, similar to shading used on Figs. 3, 4, 6.
L267: change to ‘pronounced seasonality in velocity simultaneously with a surge…’
L285: to avoid any ambiguity, I suggest changing the wording to ‘A significant variation in quiescent velocities cannot be detected…’ (at least I assume that’s what you’re referring to in this sentence)
Fig. 16: this new figure is very helpful!
L385/6: change ‘hydrological surge’ to ‘hydrological mechanism’
L403 & L408: these arguments would be more convincing if you can demonstrate that crevasses on the glacier actually changed over the periods that you describe. I know that you mentioned earlier that the resolution of Landsat imagery is insufficient to detect these changes, but have you tried looking at higher resolution free imagery from sensors such as Sentinel 2 or Planet? From my own quick search of Planet imagery, for example, there are many good scenes available since 2016, at resolutions as high as 3 m, which show clear crevasse patterns.