Seismic and piezometric signature of the natural drainage of the Tête Rousse glacier, august 9th 2025

The Tête Rousse glacier, located in the Mont Blanc massif (French Alps), is a polythermal glacier that hosts a water pocket in the center that has been identified and monitored since around 2008 [1,2]. Despite repeated artificial pumping operations aimed at draining this cavity, it continues to retain water  and is therefore subject to regular monitoring, notably through piezometric pressure measurements, Nuclear Magnetic Resonance (NMR) surveys and ground-penetrating radar profiles. This water storage may develop into catastrophic glacial lake outburst floods (GLOF), threatening infrastructures and human lives downstream.

A seismic ambient noise campaign conducted in 2022 [3] revealed anomalies the upper part of the glacier, suggesting the presence of a second water reservoir with undefined contours. The NMR survey of 2023 confirmed the presence of around 50,000 m³ of liquid water beneath the upstream part of the glacier. However, additional GPR profiles and drillings have have left significant uncertainties about this new reservoir.

In August 2025, numerous concentric cracks were observed in the upstream sector of the glacier. On 10 August 2025, eyewitnesses reported abnormal activity in the glacier's outlet stream for several hours. The presence of piezometric sensors within the glacier, combined with recordings from a seismic sensor located at its centre, made it possible to accurately reconstruct the chronology of the drainage. Beginning on 9 August, a progressive increase in anomalous microseismic activity was observed, culminating in a main event of seismic magnitude 0. Subsequently, piezometric levels exhibited a two-stage evolution: first, water flowed from the upstream part to the central cavity; second, drainage proceeded from the central cavity toward the downstream part of the glacier. These hydrological transfers were confirmed by a second seismic proxy, namely variations in seismic background noise levels. Following the drainage event, abnormal elevated microseismic activity was observed for several weeks, reflecting the collapse of drained areas and the ongoing brittle deformation within the glacier, including the development of surface cracks.

These observations suggest that seismological monitoring and piezometric measurements constitute complementary and effective tools for understanding the dynamics of glacial water pocket drainage. Moreover, they provide several precursor and early-warning signals that could be used for monitoring strategies and operational alert systems aimed at mitigating this type of glacial hazard.

References:

[1] Vincent, C., Descloitres, M., Garambois, S., Legchenko, A., Guyard, H., & Gilbert, A. (2012). Detection of a subglacial lake in glacier de Tête

Rousse (Mont Blanc area, France). Journal of Glaciology, 58(211), 866–878.

[2] Vincent, C., Garambois, S., Thibert, E., Lefèbvre, E., Meur, E. L., & Six, D. (2010). Origin of the outburst flood from glacier de Tête Rousse in

1892 (Mont Blanc area, France). Journal of Glaciology, 56(198), 688–698.

[3] A. Guillemot, N. Bontemps, E. Larose, D. Teodor, S. Faller, L. Baillet, S. Garambois, E. Thibert, O. Gagliardini, C. Vincent : Investigating Subglacial Water-filled Cavities by Spectral Analysis of Ambient Seismic Noise : Results on the Polythermal Tête-Rousse Glacier (Mont Blanc, France), Geophys. Res. Lett. 51 e2023GL105038 (2024).