|I have complete my review of the revised version of “Topographic disequilibrium, landscape dynamics and active tectonics: an example from the Bhutan Himalayas”. Generally the manuscript is greatly improved and most of my large scale comments were suitably addressed from my initial review. I have a few minor thoughts for the authors, but nothing that should preclude the acceptance of this after a few tweaks (or maybe without a few tweaks depending on how the authors feel about my thoughts).|
L324: This is a pretty minor quibble, but I’m not sure how smoothing is significant for the calculation of chi? Ksn, sure, but as long as the smoothing doesn’t change the drainage area accumulation (which CRS shouldn’t, since it operates exclusively on the extracted stream network), smoothing should have zero impact on the calculation of chi. I think you could just be vague here since you haven’t introduced all of the metrics yet and just leave it at saying that smoothing is important for some of the metrics you’ll use.
L793-794: Though for the area-loss mechanism, would you necessarily expect the spatial consistency that you note? You end up essentially using this to favor a tectonic origin, but it seems reasonable to “kill” this idea here, i.e., the extent to which an area loss mechanism is actually consistent.
L895-890: I’m curious how much of an issue you actually expect this to be? You cite this multiple times and imply that it can be quite significant generally and for the Bhutan dataset specifically, but from the cited work, this seems the most problematic for very small basins (e.g., <10 km^2) that are eroding very slowly (with the added caveats of things like erodibility, diffusivity, etc. playing a role). For the data from Adams et al 2016, while some basins are eroding reasonably slow, most of the basins (both the slow and fast eroding ones) are within the size range where this previous analysis suggests that the E/U ratio should be quite close to 1. It’s fair to point out that this could be an issue given the documented divide instability you provide here, but it’s also important to be honest about how much of an effect you actually expect this to impart, i.e. is the level of distrust you indicate we should have toward this aspect of prior work warranted? At least a qualitative assessment of this should be quite doable since many of the same authors appear on the 2019 paper as this one. This has a little bit of overlap with my comments on the first go around, i.e., that some of the criticism here of prior work seems a little overly harsh. Your study easily stands on its own merits without casting unnecessary aspersions on others work. If you can demonstrate that the majority of basins in previous published datasets may be dramatically influenced by the changes in drainage area and systematically would change the result of what was argued previously, that's one thing, but I think you should either (1) attempt to do this or (2) tone down your criticisms of this aspect.