Seminar by: Juliette Bonnet, PhD student, Université Grenoble Alpes, France.
Deep Meltwater Percolation Event and Thermal Impact of Refreezing at Depth: Observations from the 2025 Taconnaz Glacier Field Campaign
Abstract: Climate warming has induced widespread mass loss and retreat of Alpine glaciers, but also a progressive warming of high-altitude ice since the 1980s which is significantly enhanced by meltwater percolation and refreezing (Hoelzle et al., 2011; Vincent et al., 2007, 2020). Ice temperature, particularly at depth, plays a critical role in the stability of steep and hanging glaciers. While meltwater percolation and refreezing events are well known and accurately modeled in firn (Gilbert et al., 2014 ; Mattea et al., 2022), their occurrence and thermal impact within deep cold ice remain challenging to model, despite evidence of their existence (Gilbert et al., 2020; Seguinot et al., 2020). To better understand and model deep percolation through cold ice, we have designed a field campaign dedicated to directly observing such events.
During summer 2025, we conducted this campaign on the cold and highly crevassed Taconnaz hanging glacier (Mont Blanc Massif, France), where two ~85 m deep boreholes were instrumented with an optic fiber connected to a Distributed Temperature Sensing (DTS). This setup provided exceptionally high-resolution spatio-temporal measurements of ice temperature (20 cm spatial and 15 min temporal resolution). On 6th July 2025, we observed a deep meltwater percolation event marked by a sudden thermal anomaly between 55 and 70 m depth, with temperature increases of up to 5°C. This anomaly manifests as localized layers where ice temperature approached the melting point, interpreted as the rapid arrival and refreezing of liquid water near the borehole. The fine-scale spatial structure and temporal evolution of these layers provide quantitative constraints on the percolation and refreezing process. Using a thermal model, we estimate both the distance to the percolating water vein and the volume of water involved.
In addition, a network of nine seismometers operating at 500 Hz recorded the signal associated with the formation of fractures through which water was delivered at depth. That highlights the potential of seismology to detect, quantify, and localize such events at the glacier scale and to characterize the fracturing processes enabling deep water penetration.
The event caused a persistent thermal warming (~0.5 °C warmer at the end of the summer), demonstrating that deep meltwater percolation is a rapid and efficient heat-transfer mechanism that should be explicitly included in glacier thermal models and hazard assessments.
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The GeoHyd seminars are normally held in Auditorium 2 in the Geology Building, Blindern (map) but it is also possible to follow some of the seminars on Zoom.
Videolink to the lectures will be sent to the e-mail list geohyd-alle@geo and geohyd-info@geo. If you want to subscribe to the geohyd-info@geo mailing list send an email to Anita Sørlie.
About the seminar series
The talks in GeoHyd Lunch Seminar Series are offered by the Section for Geography and Hydrology (GeoHyd), Dept. of Geosciences, University of Oslo. The seminars are announced as lunch seminars so bring your lunch if you want to.
The seminars are open for everyone interested, and especially students are welcome.
The Lunch Seminar Team
– Regine, Andi and Anita