| 16 Oct 2025
Influence of water extraction on subglacial hydrology and glacier velocity
Abstract. Subglacial water modulates glacier velocity across a wide range of space and time scales by influencing friction at the glacier bed. Observations show ice acceleration due to supraglacial lake drainage and water draining through moulins, where both configurations involve water inputs to the bed. Here we consider the reverse: water extraction from the subglacial system. Removing subglacial water results in different dynamics than injecting water, and we hypothesize that understanding these processes will allow for improved characterization of the physics of subglacial hydrology. Water extraction is a proposed intervention method for slowing glaciers that requires significant further investigation before it should be tested or implemented in the field. Here we set up model experiments in the Subglacial Hydrology And Kinetic, Transient Interactions (SHAKTI) model coupled with the Ice-sheet and Sea-level System Model (ISSM). By analyzing the problem of an isolated borehole in a background pressure field to determine the region of extraction influence, we find an analytical solution which shows that the water pressure returns to the background value approximately as a logarithm with distance. The benefit of the analytical solution is that the dependence of uncertain parameters is clear and may be used to constrain subglacial hydrology models. We find good agreement between this analytical result and full SHAKTI simulations. Using the coupled SHAKTI-ISSM model, we perform transient model experiments on an idealized tidewater glacier geometry and on Helheim Glacier in Greenland to determine the effects of water extraction on glacier velocity. With continuous pumping, we simulate a modest impact on velocity, which is sensitive to the extraction rate and site location. The response time to pumping initiation and the recovery time following cessation scale according to effective pressure, with typical times on the order of hours to days. These results are encouraging that water extraction is a method of probing the subglacial hydrologic system to better constrain the uncertain physics, with further research required to determine if it is an effective intervention method.
Review of Meyer et al. (2025)- The Cryosphere
‘Influence of water extraction on subglacial hydrology and glacier velocity’
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This paper presents modelling work investigating subglacial water extraction, first of idealised simulations and then applied to Helheim Glacier, Greenland. Overall, the work provides important first steps into understanding the possible influences of water extraction on glacier velocity by examining a specific case of wintertime extraction. The work is extremely relevant to the community and suitable for publication of The Cryosphere. However, it needs some substantial re-framing to clearly state the contribution to the field and limitations of the work.
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General comments:
The title of this paper is too general to represent the contents of the article accurately. The scenarios examined are very specific (e.g. wintertime only) and this should be acknowledged in the title. The influence of water extraction goes far beyond this work.
The level of mathematical detail here was appreciated, but I found it frequently to be at the cost of the ease of understanding of the paper overall. For a journal such as The Cryosphere it should be possible for a reader without a detailed mathematical background to still understand the overall study, but the details of the simulations run and their purpose are often lost in the weeds of the mathematical solutions.
The authors frequently do a good job of stating the assumptions made and the limitations of this work in the main body of the text. They do, however, then jump to much more general conclusions that go beyond what their results show in the discussion section. The results do not suggest that water extraction can slow glaciers, except under very specific circumstances. More work is needed to determine if glaciers can be slowed under realistic scenarios (i.e. with summer melt). The paper is a little inconsistent in sometimes doing a good job of being realistic about the results (i.e. that more modelling work is needed) and sometimes making broader statements that could be taken out of context.
While the authors state that the practical, moral, ethical implications of field testing are not considered, the fact that possible future field deployment is mentioned and the location studied has a local population should not be ignored. Can the authors please acknowledge the Indigenous population of Greenland and their rights to decide about possible future field testing that happens in their home.
The authors have acknowledged that two of them have connections to the Arête Glacier Initiative, yet describe this as ‘focussed on sea level rise’ whereas Arete’s home page states ‘Arête is leading sea-level rise forecasting and glacier stabilization efforts’. While it is appreciated that the authors are declaring this interest, the fact that this is an initiative with a specific goal to research glacier stabilization should be made clear. For a topic that has attracted a lot of controversy to the cryospheric community 100% openness is essential.
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Specific line by line comments:
Line 71- Could the authors please expand on why the Theis method would be expected to be applicable to a subglacial environment e.g. as presumably this evolves much more quickly than a groundwater system
Line 105 (equation 1)- How much does the choice of sliding law matter here? Given it’s directly proportional to N it seems quite important.
Table 1- This would be much easier to follow if the parameters were also named as for anyone not familiar with SHAKTI there is a lot of back of forth to try and understand the equations.
Line 134- Does the continuous pumping assume no movement of the glacier (i.e. connection to the bed at the same place)? How might that impact future work that looks at feasibility of keeping drill holes open?
Line 146- I got a little confused between q, q and if these equations are looking at total water flux from the whole circle in figure 2 or just water movement across the boundary at the circumference. Possibly the above suggestion of making parameter names clearer might help with this,
Line 187/ Figure 4- More details about the simulations carried out here would be helpful, is this revisiting simulations from another paper? There aren’t any other simulations plotted previously.
Line 369- This is a very minor impact, but is described as a ‘modest’ impact in the abstract which is overstating 0.5-1%.
Figure 10- Can the authors please explain what is happening around day 90, and what the small fluctuations in the effective pressure are showing?
Line 377- Can you see the reconfiguration of the drainage network with SHAKTI?
Line 379- typo
Line 417- The results don’t show this, they show it can slow them under winter conditions only.