the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Aug 2026
The thermal regime of the Whymper hanging glacier under climate change (Grandes Jorasses, 4050 m a.s.l., Italy)
Abstract. Glaciers in the European Alps are typically cold above ~3500–3800 m a.s.l., which allows the formation of steep hanging glaciers. Rising air temperatures and increased surface melting are now altering their thermal regime, raising questions about when and where their bases will start to thaw which could potentially cause them to destabilize. In this study, we report unique observations of long-term temperature change (1997–2021) on the Whymper hanging glacier (4050 m a.s.l.) located on the southern side of the Grandes Jorasses (Italy). Using a state-of-the-art thermo-mechanical model and heat-flux calculations for the entire Grandes Jorasses range, we find that the observed significant temperature changes are driven by rapid surface warming since the 1990s, due to enhanced melting which has ultimately produced persistent temperate surface conditions over the past decade. Remarkably, we demonstrate that the cold basal condition will persist for several years sustained by strong negative heat flux from the colder north face of the Grandes Jorasses, though it may approach melting point temperature by 2050. However, this evolution depends on the amount of water that will percolate through ice fractures at depth, a poorly understood process that could accelerate warming. This underscores the need for continued ice-temperature monitoring in the future.
- Preprint
(5084 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-4058', Anonymous Referee #1, 09 Oct 2026
-
RC2: 'Comment on egusphere-2026-4058', Martin Lüthi, 26 Oct 2026
Dear Collegues
First, I apologize for the late submission of the review (which was
delayed by a small surgery at the start of the semester).The manuscript presents a very nice and in-depth study on the thermal
regime of a dangerous hanging glacier that has caused several large
ice avalanches in the past. By detailed numerical modeling of all
relevant processes the authors reach differentiated conclusions that
are of high relevance. These results are compared to an outstanding
set of data from boreholes in this extremely exposed glacier, a feat
that cannot be estimated high enough (and generally is not
acknowledged appropriately). So, I was glad to read this manuscript
which should be published with a few minor clarifications listed below.The part I was struggling with most is the description of the
different models. Figure 2 is a good attempt to visualize the
interrelations, but I was still confused by both the naming of the
models, and also by missing descriptions of the equations.First, the different models should be given more meaningful names than
"sub-grid" or "3D". Maybe "heat flow model", "glacier flow model",
"surface process model" or similar.Second, in the Model Description Section 2.4.1 the equations for the
Gagliardini-Meysonnier firn flow model could/should be given (I
understand some version of this was used). At present, the fuctions
a(\rho) and b(\rho) appear in Table 3, but without any context. Are
they the same as in the original publication?To add to my confusion, in line 201 Glen's flow law is invoked, so
that it is not entirely clear which flow law has been used. Also
suddenly there are results for modeled firn density. Maybe I missed
it, but the only equation about firn is the one in Figure 2, but this
is not about viscous compaction. Has firn density been calculated by
the G-M flow model? And does it feed back into the flow model by its
changing rheology?Other than this, I find the paper in a good shape. The figures are
easy to understand and nicely crafted, and the bibliography is in a
good shape. There are a few small typos and grammar errors (termial
"s") that I indicated in the comments below.To conclude, I recommend that this manuscript be published after these
points have been addressed by the authors.Best regards
Martin Lüthi
Specific Commentsl 21 I am unhappy with the term "imbalance of forces". That would mean
immediate acceleration due to Newton's second law, but is likely
not what is meant. Better call it "redistribution of stresses",
or "changes of the stress state", or similar. Even the "collapse"
is usually a slow process of gradual material disintegration
(damage), until the moment when ice is released from the glacier.l 23 "From when on" or "Knowing the moment when..."
l 32 this was already done in Lüthi and Funk (2001).
l 37 it is Italian: Colle Gnifetti
l 68 "ETH Zurich" is the name of the institute, no need for parentheses.
Fig 1 The diamond shape is used for 1997 data in panels e-h, but not
in (a) and (b), where dots are used. It would be desirable to
use the same symbols consistently in all plots. Also indicate
borehole numbers with the same color in the panels e-h.Caption: "borehole locations" (plural is on locations)
"measurement" -> "measurements"79 "velocities observations" only one plural -> "velocity observations"
Table 1: Coordinates should be aligned. Since no tens of meters are
given for 1997 data, you have to add a "\ " empty space, or
chose a reasonable Latex table formatting option.Table headings should not say "UTM32". Better give this
correctly in the caption as "UTM-32N (EPSG: 25832).Fig 2 The blue text in the left panel is too small. Also the red text
next to the arrows.Fig 2 Should the boundary condition for T or heat flux be added to the
right panel in the enthalpy?Fig 2 The mass conservation equations seems wrong.
Tab 2 Make the lines the same length, by putting the reference to
Aschwanden in the caption. You could also write out "eq."
Tab 2 is P positive or negative? p = -1/3 tr(sigma)??Tab 3 use \exp for proper typesetting, and also \frac{\rho}{\rho$_{i}$}
Tab 3 the flow rate factor is not Arrhenius, only the temperature part,
but with two activation energies, depending on temperature (Smith & Morland)Tab 3 Give Clausius-Clapeyron in MPa. Where do you get all these
digits from? Often on cites Harrison, and that number is very
approximate. For pure water, the number is very different.Tab 3 write 6.11\times 10^2 as 611
Tab 3 why don't you ignore triple point pressure, when your pressure range is 0.1-1 MPa??
Tab 3 What is the enthalpy of fusion? Is this not just latent heat of fusion?109 The *thermal* surf. bound. cond....
112 refreezes
113 reaches *the* melting point
114 for *a density* below
117 surface mass balance (lower-case)
121 "sub-grid model" should better be called "surface process model"
or similar. Also use consistent spelling (sometimes there is no dash).128 why is it called z_Dir, better use z_D or z_w (w for water)
133 Which 3D model, thermal or mechanical? Use better names for the different models.
135 *consists*
139 "resolved" should be replaced by "solved for"
140 "defined from" -> "constructed from measurements"
140 "made from" -> "based on ground radar measurements"
Table 3: use \exp for the function name
147 "no-sliding condition" or clearer: v=0 Dirichlet condition
150 consitently also use symbols, so this would be H=T_surf ??
152 this is unclear, why zero normal flux in the ice? The heat flux
should be continuous between rock and ice.154 "serves"
158 "parameters"
159 "heat flow" instead of "heat flux" ??
166 and Fig 4b Why at 50 cm depth? This is in the domain where
seasonal changes are huge, and cannot be used as a meaningful
boundary condition. Are seasonal changes matched?169 style question: I would replace \times by \cdot or nothing, like
in normal mathematical notation.172 This value seems very high for a mountain where melting ice in
within the rock likely consumes most geothermal heat flux (e.g.
Lüthi & Funk, 2003).177 "horizontal from"
188 use "strong" instead of "rapid" (which has a meaning of rapidly
with time).189 "rising": again is this changing with time? Otherwise use
"increased" or "stronger"191 "comprised" -> "in the range of..."
196 "steady conditions"
197 "happened" --> "occured"
201 Now I am confused: are you using Glen or Gagliardini-Meysonnier?
203 If a 30% higher flow rate is needed: is this due to the firn, if
an ice rheology (Glen) has been used? Or a firn rheology? How was
the firn profile modeled, by a coupled density - flow model?212 "each profile" or "all profiles" (grammar)
216 "temperatures tend" or "temperature tends" (grammar)
250 "another approach"262 "both sides"
274 I think you mean "should be accounted for" (since I believe you
know how your model works)277 You could even invoke damage again here, since failure is rarely
just local, but a stress corrosion for which a damage model is
perfectly suited. This would also allow you to calculate time
scales and velocity thresholds that should be considered
dangerous.287 Valle d'Aosta region, Lepontine Alps region (Val Ferret is very specific)
291 (grammar) "significant temperature differences" or "a significant
temperature difference"294 Easier to understand would be: "a basal cooling by a strong heat flux"
(negative heat flux is not so clear to everyone).Citation: https://doi.org/10.5194/egusphere-2026-4058-RC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 245 | 187 | 84 | 516 | 79 | 80 |
- HTML: 245
- PDF: 187
- XML: 84
- Total: 516
- BibTeX: 79
- EndNote: 80
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Dear authors, dear editor,
Thank you for this interesting manuscript on the thermal regime of the Whymper hanging glacier. Repeated englacial temperature measurements at such a hazard-relevant site are rare and valuable, and the study is in my view well suited for The Cryosphere.
My detailed review is provided in the attached PDF. It contains a summary, five general (major) comments and a list of specific (minor) comments with line references. In brief, my main points concern (1) the constraint, temporal evolution and sensitivity of the north-face heat flux, (2) the representation of deep water percolation, the scenario dependence of meltwater supply and the 2050 simulation horizon, (3) the quantitative model–data evaluation and the comparison of non-co-located 1997 and 2021 boreholes, (4) the documentation of the observational data (provenance and measurement methods), and (5) the structure of the manuscript.
I recommend major revisions and look forward to reading the revised version.
Kind regards