Dear editor and dear authors,

I have read the manuscript entitled "Time-varying drainage basin development and erosion on volcanic edifices" submitted to Earth Surface Dynamics. The manuscript attempted to propose a new conceptual model regarding transition of drainage systems regarding volcanic edifices on the basis of combinations between topographic analysis and ages of volcanic edifices. The topic is well fit for the scope of the journal and the analysis is comprehensive. The idea and analysis are novel, and thus, this study has the potential that improve understanding of landscape evolution in volcanic drainage systems on the basis of geomorphological knowledge accumulated by focusing on non-volcanic fluvial systems. However, to accept wide readers not only geomorphologists but also volcanologists, the authors should address the below my doubts.

1) The authors do not explain reasons why geomorphic and geometrical investigations regarding volcanic edifices have not been carried out well so far. In volcanic edifices, sediment erosion by fluvial processes and sediment supply by eruptions repeatedly occur in various time and spatial scales. Depending on the rate, extent, and pace of these sediment erosion and supply processes, the permeability of volcanic edifices spatiotemporally changes. Moreover, supplied-sediment properties (e.g., grain size and density) have large variations among eruptions even in a single volcano. These mean significant differences in sediment regime of volcanic drainage systems in comparison to general fluvial channels in non-volcanic basins, potentially hampering the direct use of geomorphic and geometric metrics that are developed based on observations in non-volcanic systems. Some metrics used are modified to apply investigations in volcanic edifices, but it seems that the above issues are not completely described in the Introduction section. Additionally, the history of sediment dynamics and eruptions of the respective volcanoes should be well described to support understanding of the current drainage and sediment-transport systems.

2) A total of 12 volcanoes are investigated but only 9 volcanoes are available to use deriving regressions. Additionally, the authors focused on only closely-spaced sets of volcanic edifices, but its reason is not well described. The presented analysis approach can be applied to other volcanoes. For example, the set of Mt. Sumel, Kawi, and Arujuna which are located in the east of Mt. Merapi that the authors analyzed can be candidates. I struggle to find why the authors did not analyze more volcanoes despite the use of global topographic data. Readers would doubt why the authors excluded the volcanoes in the Cascade Range despite the metric used (eroded volume) was developed based on them in the author's previous study (https://www.frontiersin.org/articles/10.3389/feart.2023.1150760/full). To support the argument that "a generalized morphologic age of an edifice may be derived that quantifies the erosional state of the landform and relates to the edifice’s lithologic age" (L200-202), a wider analysis should be done. Because volcanoes have variations in the rate, extent, and pace of these sediment erosion and supply processes as mentioned above, this lack of enough samples may not be adequate for deriving a new conceptual model.

3) Another concern is bias due to volcano sizes. The size (area) of volcanoes tended to be larger as the value of age of activity (YPB) decreased. Indeed, Kaitake (YPB = 669,627), Pouakai (YPB = 351,994), Ungaran (YPB = 387,298), and Linkruanga (YPB = 160,623) have relatively small areas compared with other volcanoes such as Merapi (YPB = 173). This aspect links with the presented conceptual model in terms of the decreasing elevation of edifices that accompanies a decrease in the corresponding area size. In this context, my doubt is that volcanoes with low elevations and large areas surrounded by the edifice boundary defined by the authors can exist. If those cannot exist, reliability and robustness of the author's argument and presented model are strengthened.

4) In the presented conceptual model (Figure 5), in all ages, volcanoes with a single summit are considered. However, as shown in Figure 9d, in Kaitake (late-stage volcano), the basins drain from the different summits. This may be similar in Pouakai. The fundamental difference regarding the drainage regime is an important aspect, but not considered well. Most volcanic summits would potentially experience collapse in a geological timescale. If so, the related changes in the drainage system can be a general process and also should be touched on in the manuscript. Moreover, the definition of basin outlet is different between early- and late-stage volcanoes. In Merapi (early-stage volcano), because the outlets of summit basins nearly correspond to the edifice boundary, the basins have elongated oval shapes (Figure 9b). In Kaitake (late-stage volcano), the outlets of summit basins are probably located at the outside of the edifice boundary, and consequently, the lower areas of some basins are linearly cut. In another late-stage sample (Likuruanga), the lower ends of basins are constrained by flowing into the sea (Figure 1b). These differences can be responsible for the bias of results in the analysis regarding basin morphology (i.e., Figure 3).

5) Many contents in subsections 4.2, 4.3, 4.4, and 4.5 should be placed in the methods or results sections. This mixing causes confusion. The manuscript should be reorganized to improve its presentation and coherence.

Minor comments

L61 complimenting -> complementing?

L62 The authors should highlight this study focuses on only stratovolcanoes throughout the manuscript.

L72 Please explain the reason why only closely-spaced sets were focused.

L74-75 Please explain the reason for this exclusion.

L77 Because van Wees et al. (2021) is an abstract rather than a paper, readers cannot follow the method used here.

L83 More clear and robust explanations are necessary.

L86-87 Is this a reason for the volcano selection?

L123-125 Please refer to Figure S2 and Table T1 effectively.

L187-188 Eroded volume is not a general metric. Thus, a brief description is required.

Overall: This is a very interesting paper that creates a solid framework for understanding the interplay between volcano construction and volcano degradation.  Surprising results include the co-decrease of height and radius (although height is faster) and the decrease in normalized slope variance with age. The later was surprising because I think of scoria cones (the volcanoes I'm most familiar with) as getting rougher over time (more deep incisions) but understand that the increase in the mean slope is driving the increase in the term. 

The most valuable contributions of this work include (a) the port of MorVolc code to Matlab, which is greatly appreciated,  and the sharing of that and DrainageVolc through GitHub and (b) the development of a new measurement of slope variance, which seems promising for quantifying the changes in volcanic landforms, large and small. The visual shifts and differences are often apparent in both topography and photos but have not been previously quantified.  

My main caveat or disagreement is that I am not sure the mean eruptive age of a volcano is indicative of its landform development state. I would have expected the landform to reflect the last significant eruptive activity. 

Finally, here are the questions would I like answered in the manuscript: What is the minimum size of volcano considered? Were all volcanoes considered classified (or classifiable) as composite or stratovolcanoes? What are “sinks in the DEM” and why do they need to be filled? The first two questions concern how applicable these results are to volcanoes in general as opposed to just the larger stratovolcanoes or composite volcanoes that dominate landscapes.  The later may be displaying my ignorance of GIS processing (if so, a simple reply rather than manuscript edits would suffice).

References seemed adequate although I’m unfamiliar with the geomorphology literature.

I have no specific line by line comments - the grammar and typography were fine as is and figures great.