Mapping the cold-temperate temperature transition at the base of Taconnaz hanging glacier using multi-data analysis.

5 ou 6 mois à partir de février 2027

Context :
The stability of steep hanging glaciers is largely influenced by the temperature at the ice-rock interface, which has a significant impact on basal friction when it reaches the melting point. High-altitude glaciers are currently warming in response to rising air temperatures and increasing surface meltwater production (Vincent et al., 2020). The rate at which this surface warming will propagate to the glacier base can be estimated using three-dimensional thermo-mechanical modelling of the glacier (Gilbert et al., 2026), in order to anticipate a potential unstable state of the glacier. However, there are still significant uncertainties due to the difficulty of assessing how much surface meltwater reaches the deeper parts of the glacier through ice fractures. Recent field campaigns on the Taconnaz hanging glacier (Mont Blanc range, France) have revealed the presence of localized patches of temperate basal ice. These patches are not predicted by current models (Gilbert et al., 2015), which potentially suggests an underestimation of the rate at which the basal ice is warming. The current extent of this temperate ice remains thus uncertain, even though the Taconnaz Glacier is a benchmark glacier for modelling thermal regimes, and its instability poses serious threat to the Chamonix Valley.

Internship objective and method :
The aim of this internship is to map the current extent of temperate basal ice of Taconnaz glacier in order to improve models and future predictions of basal thawing. This map will be determined by combining different datasets including remotely sensed surface velocities, on-site continuous GPS measurements, borehole temperature profile measurements and ground penetrating radar measurements. Each dataset will provide an estimate of where temperate ice can be found, and combining all the results will produce a map showing the likelihood of a given area having a cold or temperate basal temperature.
1 - Seasonal surface velocity maps derived from high-resolution Pleiades satellite data will be used to infer seasonal changes in basal sliding velocity. For each surface velocity map, the basal friction coefficient will be inverted to identify areas of temperate ice where sliding occurs and varies over time.
2 – A similar analysis can be done from surface GPS measurement acquired during summer 2026.
3 – Scatter in Ground Penetrating Radar (GPR) can be used to identify temperate ice (Gilbert et al., 2020).
4 – Spatial interpolation between measured basal temperatures in boreholes can also provide potential constraints on the location of temperate ice.

Task of the internship :
1 – Perform basal friction inversion using Elmer/Ice (Gillet-Chaulet et al., 2012) on each Pleiades surface velocity map
2 – Analyze the GPR profiles to determine potential temperate ice
3 – Analyze the seasonal velocities recorded by on-site GPS data
4 – Combine all the information to produce a map showing the likelihood of temperate conditions at the glacier bed.

References :
Gilbert, A., Vincent, C., Gagliardini, O., Krug, J., & Berthier, E. (2015). Assessment of thermal change in cold avalanching glaciers in relation to climate warming. Geophysical Research Letters, 42(15), 6382–6390. https://doi.org/10.1002/2015GL064838
Gilbert, A., Sinisalo, A., Gurung, T. R., Fujita, K., Maharjan, S. B., Sherpa, T. C., & Fukuda, T. (2020). The influence of water percolation through crevasses on the thermal regime of a Himalayan mountain glacier. The Cryosphere, 14(4), 1273–1288. https://doi.org/10.5194/tc-14-1273-2020
Gilbert, A., Troilo, F., Gagliardini, O., Vincent, C., Perret, P., Mondardini, L., et al. (2026). The thermal regime of the Whymper hanging glacier under climate change (Grandes Jorasses, 4050 m a.s.l., Italy). EGUsphere, 1–22. https://doi.org/10.5194/egusphere-2026-4058
Gillet-Chaulet, F., Gagliardini, O., Seddik, H., Nodet, M., Durand, G., Ritz, C., et al. (2012). Greenland ice sheet contribution to sea-level rise from a new-generation ice-sheet model. The Cryosphere, 6(6), 1561–1576. https://doi.org/10.5194/tc-6-1561-2012
Vincent, C., Gilbert, A., Jourdain, B., Piard, L., Ginot, P., Mikhalenko, V., et al. (2020). Strong changes in englacial temperatures despite insignificant changes in ice thickness at Dôme du Goûter glacier (Mont Blanc area). The Cryosphere, 14(3), 925–934. https://doi.org/10.5194/tc-14-925-2020