Dear colleagues,

Congratulations for this original work on tsunami hazard from underwater explosions in Lake Taupo. The manuscript represents a substantial contribution to hazard assesment in the Laker Taupo area, and the recent tsunami observed on November 30, 2022 shows how this study is timely (although the source of the tsunami is not yet elucidated). The overall quality of the scientific and methodological approach is very good, and the results are presented in a clear and concise way. The manuscript is well-written and well-illustrated. I have only some minor comments that are listed below:

- The use of the Volcanic Explosivity Index VEI (e.g. at lines 8-9, 264, 266, 320-324, 371) is not fully appropriate here, because it is based only on the total erupted volume. Here you are dealing  with short discrete explosions. You can keep the VEI values in Table 1, for information. However I would recommend refering to the energy or mass eruption rates in the text.

- I suggest adding a sentence on the tectonic setting, which is too briefly mentioned at line 24: "The 350 km-long TVZ forms the southern part of a back-arc basin behind the Tonga-Kermadec subduction zone. Most of the eruptive centres are aligned along the intra-arc Taupo rift."

- The TVZ cannot be considered as a purely silicic magmatic system, because the magmas erupted range from andesites to rhyolites.

- At line 169 you state that "the water and explosion depths are equivalent." This is valid only in the case of a new vent formed on flat lake bottom. If the explosion comes from a pre-existing submarine cone, then explosion depth and water depth are not equivalents. This statement should therefore be qualified.

- I suggest slightly reorganizing the paper as follows:

        3. Results

        3.1. Tsunami propagation and wave heights at the coast

        3.2. Tsunami inundation and potential impact on infratructures

- In the discussion, we lack a short discussion (at line 324?) on the probabilities mentioned on Table 1, in the light of the new results obtained here.

- The scenario presented at lines 330-334 is very pragmatic and relevant. Indeed in the case of such an eruption, all people would be probably evacuated before a tsunami could impact them. Could you add a short sentence of the consequences in terms of evacuation policies?

- In the conclusion, maybe you could formulate some recommendations for a local tsunami warning system in Lake Taupo?

Line-by-line corrections/suggestions:

-line 7: "This minimum size corresponds to..."

-9: "slope" rather than "runu-up"?

-37: "(HTHH, January 2022)"

-37: You could cite other references on the HTHH tsunami (e.g. Carvajal et al., 2002; Omira et al., 2022).

-41: cite also Maeno & Imamura (2011) for the 1883 Krakatau tsunami debate.

-56: "and in the present work it is..."

-59-63: this sentence is perhaps too long.

-93 refined against what?

-127: 7% of what?

-128-129: not sure if these lines are really useful here.

-194: "'We selected the five..." 

-230-232: again, this sentence is a little bit long.

-248: refer to Fig 6 (c-d).

-257: 1 m instead of 1 cm?

-340: "asteroid-ocean impact, megatsunami from ocean-island flank collapse, and the recent tsunami..."

-345: "over half a decade old " -> a reference is needed here.

- 350-352: I was quite surprised that you don't cite here the work of Shen et al. (2021a, 2021b).

-367: "of what any tsunami hazard"

-384: What is the address of the website where Basilisk can be found?

Suggestions on figures:

- change the color of the eruption sites on figure 2 (white or yellow?).

- Fig 4: add source location (eruption sites) on the maps (same for fig 5).

- On the left side of fig 4, could you please mention the location number (1 to 5) as in Table 2, for more clarity (same for fig 5).

- Fig 6: add a dotted line to indicate the 1 m threshold value?

- Fig 6 c) d): in the caption, indicate that the first numbers refer to the scenarios and the name to the source locations 1 to 5.

- Fig. 8: Indicate to which closest source it corresponds on the different maps (same for fig 9).

Suggested references:

- Carvajal, M., Sepúlveda, I., Gubler, A., Garreaud, R.(2022). Worldwide Signature of the 2022 Tonga Volcanic Tsunami. Geophysical Research Letters, 49 (6), art. no. e2022GL098153; doi: 10.1029/2022GL098153

- Omira, R., Ramalho, R.S., Kim, J., González, P.J., Kadri, U., Miranda, J.M., Carrilho, F., & Baptista, M.A. (2022). Global Tonga tsunami explained by a fast-moving atmospheric source. Nature; doi.org/10.1038/s41586-022-04926-4

- Maeno, F., Imamura, F., 2011. Tsunami generation by a rapid entrance of pyroclastic flow into the sea during the 1883 Krakatau eruption, Indonesia. Journal of Geophysical Research 116, B09205

- Shen, Y., Whittaker, C.N., Lane, E.M., White, J.D.L., Power, W., Nomikou, P., 2021a. Laboratory experiments on tsunamigenic discrete subaqueous volcanic eruptions. Part 1: Free surface disturbances. Journal of Geophysical Research, Oceans 126, e2020JC016588.

- Shen, Y., Whittaker, C.N., Lane, E.M., White, J.D.L., Power, W., Nomikou, P., 2021a. Laboratory experiments on tsunamigenic discrete subaqueous volcanic eruptions. Part 2: Properties of generated waves. Journal of Geophysical Research, Oceans 126, e2020JC016587.

The article discussed the possible hazard caused by volcano eruption at Lake Taupo through numerical simulations. The manuscript is well-written, and the overall quality of the scientific approach is very good, and the results are presented clearly. As a numerical modeler, I have several comments on this article. 

First, what is the motivation of using MLSW for this case?

Authors used multi-layer SWE for numerical simulations, and showed that the computational efficiency of the MLSW solver is poor. Recent studies on HTHH (Pakoksun et al. 2022) showed that numerical simulations with NLSW or Boussinesq-type equations are in good agreement with the near-field observation. It would be desirable for the authors to perform numerical simulations with NLSW and Boussinesq eqs, and compare the maximum inundation heights and computational efficiency. 

Authors may argue that the waves generated by the volcanic eruption are very dispersive. However, I am not sure that Lake Taupo is large enough for the waves to develop dispersive characteristics since the waves reach the shore in 12 minutes or less. 

Second, it is unclear how the authors handled the bottom friction. 

One of the important factors for predicting current speed and Inundation height is the bottom friction coefficient. In the study of inundation by storm surges, Madli and Dawson (2014) claimed that variable friction can be important to take into account in storm surge simulations, and numerical models apply complex bottom friction fields. I would like to know how authors considered the bottom friction, and wet/dry interface for simulations. 

Comments

L59-63 unclear

L77 “have been attempted using” -> used

Section 2.1 & 2.2 are similar to Hayward et al. 2022b. Authors may shorten these parts. 

Inconsistent in the simulated time. Which is correct? L204 “All runs were executed for 24 minutes of simulated time”  L219 “All scenarios were computed until a simulated time of 1400 s”

L211 “The number of these placed along a section is set to match the maximum horizontal grid resolution.” unclear

L240 “leading to a longer duration from the first arrival to the maximum amplitude wave at greater distances from the source” unclear

L309 “For these sources, this 310 does not happen and therefore the reflection, and the incidence of troughs between wave peaks at the inlet, produces negative (or reverse) discharges from the inlet towards the lake.” unclear

L312 72% of something?

Figure 4 & 5 The information on the wave height is hard to discern from the figures. It would be better to plot the maximum wave height along the perimeter of the lake (in 2-D)

References

Pakoksung, Kwanchai, Anawat Suppasri, and Fumihiko Imamura. "The near-field tsunami generated by the 15 January 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano and its impact on Tongatapu, Tonga." Scientific reports 12.1 (2022): 1-15.

Mandli, Kyle T., and Clint N. Dawson. "Adaptive mesh refinement for storm surge." Ocean Modelling 75 (2014): 36-50.