Dear Reviever,

thank you for your comments! Please allow for some short responses before addressing your points later in a detai.

The theory may indeed be quite tough for "average" geologists. This is why I used a somehow unusual structure (not "Methods", "Results", ...) with two sections (2 and 3) developing the new ideas and already illustrating them with examples. Section 4 becomes more difficult since combining process parameters to length scales (lambda) or to nondimensional proporties (energy rate, epsilon) is not widely done in geology. The consequence is that readers who want to understand why the modified rheology reproduces the scaling of H/L with volume quite well have to go through it step by step. I know that not many readers will do this, but I think that it is not a big problem. As you suggested, I already prepared a schematic cross section that illustrates the geometric properties (H,l,beta,h,S,L). This will probably help to keep track of the variables. I can also check where I can add more explanations to the theory, but overall, it will still be a challenging paper for the majority of the readers.

However, there is one aspect where I disagree to your point of view. It looks a bit to me as if you want to promote the idea that long runout is owing to fragmentation. But even if I believe that the degree of fragmentation increases with increasing runout length, this argument cannot be reverted so easily. I know that some researchers are working on this topic, but to my knowledge is has only been shown that fragmentation can in principle increase the fluctuations in kinetic energy and thus in velocity. Overall, however, fragmentation consumes energy. I am not aware of any experimental or modeling studies that were able to predict the decrease in H/L with volume quantitatively based on fragmentation. As soon as anyone has succeeded in this, we can start the discussion whether my approach with the two flow regimes or fragmentation is better. Until then, however, just claiming that long runout cannot be explained without fragmentation (what some researchers are doing) is not a good argument for me. In turn, however, I do not want to criticize the idea of fragmentation in this paper.

Best regards,

Stefan Hergarten

Dear Matthias Rauter,

thank you for your comments! It looks a bit to me as if it was intended to be a review, but then accidently registered as a community comment. Anyway, please allow for some short responses before addressing your points later in a detail.

First, about the biggest problem from your point of view -- the sharp transition between the two regimes and the jump in friction. You consider sharp transitions "rather unphysical". In turn, I learned parsimony as a fundamental principle when I studied physics in the 1980s. Admittedly, this is long ago, but I still prefer to avoid unnecessary complications of models. The jump in friction also does not cause numerical issues since only the acceleration becomes discontinous, while the velocity remains continuous. The main effect of the jump in friction (beyond the runout length) is that the deposits become hummocky, which is not necessarily unrealistic. However, I cannot address numerical aspects in this paper since it is subject of another manuscript in GMD, which unfortunately has got stuck in the editor search for more than 2 months now.

You say that the scope of the manuscript is a bit unclear to you and mention your 2016 paper (doi 10.5194/nhess-16-2325-2016). While you say "We went trough the same exercise", the scope seems to be completely different to me. You developed a rheology that is somehow similar to Voellmy's rheology and presented a theory that goes much deeper into kinetic theory than the ideas of Salm (1993) (doi 10.3189/S0260305500011551). However, your result was that it fits for snow avalanches as well as the original Voellmy rheology. I think this is ok for snow avalanches, but it will probably not solve the problem of the long runout of rock avalanches or maybe even fail completely at large thickness. It should be clear already from the title that my approach attempts to modifiy Voellmy's rheology seriously in order to predict the long runout of rock avalanches.

Finally, your statement "I do not understand the scaling (section 4)" confuses me a bit. I realize that I lost you quite soon in this section. In turn, I know at least some of your papers and reviewed at least one of these. Since the theory presented there is much more complicated than my approach (only ordinary differential equations and exponential functions), I cannot imagine that the mathematical background is any challenge for you. I guess the extensive usage of nondimensional ratios is the main problem for you, but I am not sure. I can add a schematic diagram illustrating the variables and explain those aspects addressed in your specific comments in more detail, but I am still a bit uncertain where the fundamental problem is.

Best regards,

Stefan Hergarten