the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Volume, formation and sedimentation of future glacier lakes in Switzerland
- 1Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, 8092, Switzerland
- 2Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, 8903, Switzerland
- 3Department of Geosciences, University of Fribourg, Fribourg, 1700, Switzerland
- 1Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, Zurich, 8092, Switzerland
- 2Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, 8903, Switzerland
- 3Department of Geosciences, University of Fribourg, Fribourg, 1700, Switzerland
Abstract. Ongoing climate change and associated glacier retreat is causing rapid environmental change, including shifts in high-alpine landscapes. Glacier lakes, which can form in topographical depressions left behind by glacier retreat, are prominent features within such landscapes. Whilst model-based estimates for the number and area of future glacier lakes exist for various mountain regions across the world, the exact morphology and temporal evolution remain largely unassessed. Here, we leverage a recently released, measurement-based estimate for the subglacial topography of all glaciers in the Swiss Alps, to provide an estimate about the number, size, time of emergence, as well as sediment infill of future glacier lakes. The topographical information is based on 2,450 km measured ice thickness profiles, whilst the temporal evolution of glaciers is obtained from a glacier evolution model forced with an ensemble of climate projections. We estimate that up to 683 potential lakes with an area > 5,000 m2 and a depth > 5 m could emerge across the Swiss Alps if glaciers were to disappear completely, with the potential to hold a total water volume of up to 1.16 [1.05, 1.32] km3 (numbers and 95 % confidence interval). For a middle-of-the-road climate scenario, we estimate that about 10 % (0.12 [0.04, 0.18] km3) and 48 % (0.56 [0.26, 0.67] km3) of this volume could be realized by 2050 and 2100, respectively. In a first-order assessment, we also estimate that ca. 45 % of the newly emerging glacier lakes (260 out of 570) will be transient features, i.e. will disappear again before the end of the century owing to refilling with sediments released by glacial erosion and proglacial sediment transport.
Tim Steffen et al.
Status: final response (author comments only)
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RC1: 'Comment on esurf-2022-12', Greta Wells, 29 Mar 2022
General comments
This manuscript thoroughly discusses future glacial lake evolution in the Swiss Alps derived from newly acquired glacier topographic data. It clearly frames the study in the context of previous research, explains existing data gaps, and offers a robust methodology to fill these gaps. The manuscript adequately answers the fifteen evaluation criteria questions, scoring particularly highly on organization, explanation of methods for reproduction by other scientists, and discussing the study in relation to existing work and future research implications.
The paper does an excellent job of maintaining the balance between model generalization and case study specifics. One of its strongest features is comprehensively explaining the selection process and potential uncertainties or unknowns for each model parameter. The authors also demonstrate a firm understanding of how field variables (i.e. real-life topography, sediment, and glacier melt dynamics) are represented by model components, and how changes in field variables will influence model input parameters and results/outputs. I think such a clear link is often missing in modeling papers.
Specific comments
- Title: Maybe replace “formation” with “evolution” to imply how lakes will continue to change through time rather than when they will initially form. “Evolution” would also better describe lakes that disappear due to sediment infilling. Also consider adding the study time scale into the title—something like Volume, evolution, and sedimentation of glacier lakes in Switzerland over the 21st century.
- Do mass wasting (i.e. from surrounding slopes) and/or supraglacial debris (i.e. transferred from the glacier surface to the lake) significantly contribute to sediment infill? Maybe not, but is it worth considering?
- While the paper explains the model generalizations and parameter uncertainties for lake bathymetry, I think this point merits further discussion. For example, are variabilities in overdeepening morphologies expected at individual glaciers or between the four river catchments in the study area? Even though a thorough analysis of basin morphometry is beyond the scope of this paper, specific discussion in the context of the study area would be interesting.
- Similarly for sediment infill—the paper does a great job of explaining the model parameters/uncertainties for sedimentation rate, but I think it’s worth expanding the discussion on how local/site-specific variations may influence results. For example, are there significant anticipated differences in sedimentation rate (i.e. due to local bedrock lithology or erodibility) between the four studied Alpine catchments? Also, in section 5.2 (lines 480-484), it would be helpful to detail the type of field validation required (i.e. bathymetric surveys or sediment influx river/lake measurements).
- The figures are great, but I think the paper would be strengthened by adding a schematic diagram to accompany the sediment input graph in Figure 5. Maybe a cartoon visualization of a lake (like the cross-section shown in Figure 6) that shows the locations on the landscape of sediment source zones (headwall erosion, subglacial abrasion, and proglacial erosion). Also maybe draw upstream lakes to illustrate sediment trapping. Though the information is described in the text and existing figures, a “landscape view” would help to visualize sediment sources and transport.
- A map showing the locations of the glaciers mentioned in the text would be helpful (i.e. those in Table 1)—though I did notice that the lake polygon shapefiles are online in “data availability.”
- Conclusion (section 6): It would be nice to expand discussion of future climate change (lines 575-579) in terms of:
- Specific glacial lakes in the Swiss Alps. Based on results, do certain river catchments/glacial lakes in the study area have higher outburst flood risk, greater hydropower potential, or higher ecological relevance?
- Other glacial regions worldwide. How can this method be applied to other regions—i.e. are there any factors that make its application unique to the Swiss Alps? Even if this is beyond the scope of the paper, I think it is useful to develop this idea in a few more specific sentences.
Technical corrections
The paper reads very smoothly—these are all minor!
- Line 31: “…amongst other features" (or add a similar word)
- Line 57: Switch order: “205 additional lakes…”
- Line 62: replace “or” with “and”
- Line 68: “…once the glacier has retreated…”
- Line 85: replace “combing” with “combining”
- Line 111: “… has been shown to yield the most robust results”
- Line 114: remove “to” : "…as the “mean bedrock topography”"
- Line 134: remove “as” : "…the procedure described above."
- Line 157: maybe replace “political environment” with “policy decisions”?
- Line 174: change to “after glacier retreat" (remove “-ed”)
- Line 189: I think bedrock lithology should be included as a factor in basin erodibility
- Line 239: "The same is true when comparing the lakes…”
- Line 250: “The uncertainty in lake volume is also controlled by…”
- Line 302-303: "In the first instance, the correlation between lake size and glacier extent can be attributed to the fact that…”
- Line 305 (Figure 1): delineate the catchment boundaries more clearly on the map—it is difficult to distinguish between the Rhine and Inn basins, particularly. It would also be helpful to add an inset map showing the study area location within the larger region/Switzerland. The label “B” also does not clearly show up on the panel.
- Line 315 (Figure 2): add a temporal reference frame (what time scale does this show?)
- Line 319: remove “s” in lakes (…of each individual lake)
- Line 323: remove “a” (…provide confidence intervals…)
- Line 346: …disappear again by 2100?
- Line 349: …the rate is approximately constant…
- Line 395 (Figure 3): perhaps this is obvious and I missed it, but explain abbreviation “CH” on panel B
- Line 403 (Figure 4): explain what the grey areas denote—I assume it’s uncertainty, but clarify it in the caption.
- Line 425: "Although in terms of area and volume…”
- Lines 427-8: “…in the first place…”
- Line 432: …glacier lakes has been conducted…”
- Line 443: perhaps this is a technical term I’m not familiar with, but the word “embedding” is unclear in this sentence. Maybe replace with “position” or “formation”?
- Line 454: I think you mean plant/vegetation/floral colonization, but maybe add a word to clarify this
- Line 469: use another word besides “related”—maybe “presented”?
- Line 503: “The differences between GlaTE and ITVEO are dependent…”
- Line 516 (Figure 6): add an inset map to show the location of this site within the study area/Swiss Alps.
- Line 568: specify when “mid-term” is (mid-century?)
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RC2: 'Comment on esurf-2022-12', Jan-Christoph Otto, 19 May 2022
The authors present a study on the future evolution of glacial lakes beneath glaciers in Switzerland. While this task has been previously performed for the same study area using a comparable approach, this study adds three significant new aspects to the procedure. The authors use an ice thickness model that is based on a large data set of GPR measurements for many glaciers (1). Even though the spatial assessment of the ice thickness is still based on models, the models used here have the potential to be more close to reality compared to the previous approaches that where based on glacier surface topographies only. Furthermore (2), the approach uses an established model to simulate the release of the potential overdeepenings by modelling glacier volume changes in relation to climate change for different climate scenarios. Finally, (3) the study for the first time accounts for the potential refilling of the exposed overdeepenings by generating a time- and space-dependent approximation of the sedimentation rate at various future stages of catchment and glacier evolution. This approach tackles the highly relevant uncertainty of the true lake evolution and potentially generates a more realistic picture of potential future lakes, despite other sources of uncertainty.
The study is well laid out and the manuscript has been produced with great diligence and logic. The methods applied uses data and approaches based on various previous studies published in the recent past. Therefore, methods description is focusing on references to existing papers. Solely the approach to quantify the sediment infill rate adds a new methodological step in this study. This approach is clearly presented, even though some issues arise (see below). However, the procedure presented is convincing and represent a logical way of assessing this critical parameter of lake sedimentation, where very little data is available so far. All results are clearly presented and visualized at good quality. The discussion states the relevant and critical aspects and implications of the approach and topic in general. The authors compare their results to two previous similar studies considering a good agreement with the approach by Linsbauer et al. (2012) and larger discrepancies to the other previous study.
I consider the manuscript a valuable contribution to the issue of future evolution of glacial lakes. Especially the accounting for sediment refill adds an important new dimension and the results in relation to future glacier and sediment dynamics present highly valuable new insights into the future of glacial and proglacial sedimentary systems, despite the rather simple approximation of glacial erosion and lake sedimentation. It therefore represents a significant improvement compared to previous studies and is worth publishing. I have only few comments and minor issues to consider.
Specific comment:
Section 3.3. – I have some concerns with the use of the variable α crit in the estimation of the Sed in components. For (1) abrasion, the variable makes sense as is. For (2), increase in deglaciarized area, and (3), glacial and periglacial erosion, I would suggest to reconsider your approach or the description of it. From my understanding α crit represents the mean slope of all glaciers of the SGI2016 (L196 “α crit are critical values for mean thickness and slope that correspond to an average Swiss glacier”). For parameter (1), it makes sense to me to use an overall mean for all glacier in the equation. Here you compare h and slope of individual glaciers with overall means across the SGI2016 dataset to generate an index of abrasion, which differs between glaciers due to size and topography. However, for parameter (2) and (3) I think it would make more sense to use α crit as the mean slope of the individual glacier and not the overall mean. Since all other terms of the equation are referring to the individual glacier, I don’t understand why slope does not. Maybe it’s just a mistake in describing the equations. Please reconsider this issue.
Minor comments:
L63 add Otto et al. (2022) to the list for completeness
Otto, J.-C., Helfricht, K., Prasicek, G., Binder, D. & Keuschnig, M. (2022) Testing the performance of ice thickness models to estimate the formation of potential future glacial lakes in Austria. Earth Surface Processes and Landforms, 47( 3), 723– 741. Available from: https://doi.org/10.1002/esp.5266
L147ff – Check the phrasing here with respect to the term “mean bedrock topography” . Previously you generated the bedrock topography from the ice thickness models, now you go the other way…this does not make sense. I guess here you simply use the mean ice thickness model and not the bedrock topography. This would be in accordance to the Huss and Hock (2012) approach.
L154 – replace or with for
L188/189 – Erodibility is also affected by bedrock lithology. Sediment availability is equally important with respect to the tools required for abrasion. The former could probably not be accounted for here, while the latter is somehow represented by your consideration of headwall erosion. Please mentions these in the text.
L192 and L206ff – glacial and periglacial erosion….I would suggest to term this part solely periglacial or better headwall erosion (like you do in figure 5B), since you refer to the headwall area here only. Glacial erosion is represented by the approximation of abrasion in (1). Headwall erosion would include both processes, periglacial and feedbacks by glacial erosion.
206 – consider adding some more recent references like:
SANDERS, J. W., CUFFEY, K. M., MOORE, J. R., MACGREGOR, K. R. & KAVANAUGH, J. L. 2012. Periglacial weathering and headwall erosion in cirque glacier bergschrunds. Geology, 40, 779-782.
And/or
HARTMEYER, I., DELLESKE, R., KEUSCHNIG, M., KRAUTBLATTER, M., LANG, A., SCHROTT, L. & OTTO, J. C. 2020. Current glacier recession causes significant rockfall increase: the immediate paraglacial response of deglaciating cirque walls. Earth Surf. Dynam., 8, 729-751.
L386ff – In the methods section you described to quantify sediment infill rates in kg/m³ runoff. How do you relate these to erosion rates? (also relevant for figure 5B)
Figure 1 A: rename the legend items...it seems like you depict the total deglaciated area and not the total lake area as described in the figure caption. What does “1e6” represent at the upper left and lower right corners?
Tim Steffen et al.
Tim Steffen et al.
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