Nanni et al. (2025) Observed positive feedback between surface ablation and crevasse formation drives glacier acceleration and potential surge

Identification

• Journal: Nature Communications
• Year: 2025
• Date: 2025-12-18
• Authors: Ugo Nanni, Coline Bouchayer, Henning Åkesson, Pierre-Marie Lefeuvre, Erik Schytt Mannerfelt, Andreas Köhler, Olivier Gagliardini, Jack Kohler, Louise Steffensen Schmidt, John L. Hult, François Renard, Thomas V. Schuler
• DOI: 10.1038/s41467-025-66349-9

Research Groups

• Department of Geosciences, University of Oslo, Oslo, Norway
• Njord Centre, Departments of Geosciences and Physics, University of Oslo, Oslo, Norway
• Norwegian Polar Institute, Tromsø, Norway
• NORSAR, Kjeller, Norway
• IGE, Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, Université Gustave Eiffel, Grenoble, France
• ISTerre, Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, Université Gustave Eiffel, Grenoble, France

Short Summary

This study investigates the initiation of a surge at Kongsvegen glacier, Svalbard, by integrating two decades of multi-method observations and simulations. It identifies a positive hydro-mechanical feedback loop where increased surface melt leads to crevasse formation, enhanced meltwater delivery to the bed, increased basal water pressure, and further glacier acceleration and crevassing, driving the expansion of localized instability.

Objective

• To investigate how climatic and glacier-specific drivers interact to initiate glacier instability, specifically focusing on the recent acceleration of Kongsvegen glacier, Svalbard.
• To diagnose the dynamic consequences of climate-driven geometric changes, identify responsible surface and subglacial processes, and interpret the acceleration as a self-amplifying hydro-mechanical feedback.
• To discuss the potential for broader glacier-wide destabilization and contextualize findings within a global perspective.

Study Configuration

• Spatial Scale: Kongsvegen glacier, Svalbard (78.8° N, 13.3° E), along a 13 km central flowline. Seismic investigation is sensitive to an area of approximately 1 square kilometer around each seismometer.
• Temporal Scale: Two decades of observations and simulations, with specific data periods including 2005–2023 for some in-situ data, 2018–2023 for seismic measurements, and 1991–2022 for runoff simulations. The analysis focuses on changes from 2005, particularly the 2014–2023 period.

Methodology and Data

• Models used:
  • CryoGrid-community model (for surface energy balance and runoff simulations).
  • Stress balance diagnosis (calculating driving stress, longitudinal stress, and basal shear stress).
  • Weertman-type sliding law (to calculate bulk basal sliding coefficient, As).
  • Regularized Coulomb sliding law (to derive effective pressure and basal water pressure).
  • Forward model relating seismic power and subglacial runoff to relative changes in subglacial hydraulic radius and pressure gradient.
• Data sources:
  • In-situ Global Navigation Satellite System (GNSS) measurements (glacier surface velocity, 2005–2023).
  • Borehole and surface seismometers (seismic power in 5–10 Hz band, icequake activity in 25–100 Hz band, 2018–2023).
  • Remotely sensed surface-elevation changes (Digital Elevation Models from ArcticDEM project for 2014–2023; satellite-derived elevation changes from ref. 30 for 2000–2014).
  • Glacier bed topography map (from radio-echo sounding measurements, ref. 74).

Main Results

• From 2005 to 2014, Kongsvegen exhibited low glacier surface velocity (below 1.58 × 10⁻⁷ meters per second) and thinning (up to -5 meters near the glacier front).
• Since 2014, the glacier experienced significant localized acceleration in the upper ablation zone (kilometers 12–14), with melt-season averages reaching up to 2.54 × 10⁻⁶ meters per second in 2023. This acceleration was accompanied by continued thinning near the glacier front (up to 30 meters between 2005 and 2023) and localized thickening (up to +10 meters) in the acceleration zone.
• Basal shear stress (τb) increased from approximately 120 kilopascals in 2014 to 180 kilopascals in 2023 across most of the ablation area, but decreased from approximately 75 kilopascals to 25 kilopascals in the upper ablation area (kilometers 14–16).
• The bulk basal sliding coefficient (As) increased by one order of magnitude in the peak acceleration area (kilometers 12–16) between 2014 and 2023, reaching 2 × 10⁻²⁹ meters per second per pascal cubed.
• Basal water pressure conditions approached flotation (ratio of basal water pressure to ice overburden pressure near 1) in the area of maximum surface velocity (kilometers 12–16) by 2023, indicating reduced ice-bed coupling.
• Icequake rates in the upper part of the glacier (locations 5–9) gradually increased from approximately 0.0208 events per second in 2018 to up to 0.139 events per second in 2023, correlating with increased surface velocity.
• A positive hydro-mechanical feedback loop was identified: increasing surface melt leads to glacier surface steepening, initiating glacier acceleration, which induces increased along-flow tensile stress and crevasse opening. These crevasses provide pathways for surface water to the glacier bed, increasing basal water pressure, reducing basal friction, and further accelerating ice flow, thus perpetuating the feedback.
• The formation and down-glacier propagation of a surface bulge (local ice thickening) between 2019 and 2023, accompanied by a reduction in basal shear stress behind the bulge, are consistent with classic signatures of surge propagation.

Contributions

• Provides rare empirical evidence, through multi-method in-situ observations (GNSS, borehole and surface seismometers) and remote sensing, of the detailed hydro-mechanical processes driving glacier surge initiation.
• Identifies and quantifies a positive feedback loop between surface ablation and crevasse formation that drives glacier acceleration, highlighting a critical mechanism for glacier instability.
• Extends the understanding of this hydro-mechanical feedback to temperate-bedded glaciers, demonstrating its relevance beyond previously studied cold-based systems.
• Highlights a significant gap in current ice loss and sea-level rise projections, which often underestimate dynamic glacier responses, particularly the role of crevasse-facilitated meltwater routing and its impact on basal water pressure.
• Proposes specific avenues for future modeling efforts, including explicit calculations of tensile stresses and coupled ice dynamics-subglacial drainage models that account for crevasse-facilitated hydraulic connectivity and hydraulically unconnected bed areas.

Funding

• Research Council of Norway: MAMMAMIA (grant no. 301837), SLIDE (no. 337228), JOSTICE (grant no. 302458)
• Faculty of Mathematics and Natural Sciences at the University of Oslo: Earth-Flows
• Center for Advanced Study at the Norwegian Academy of Science and Letters: FricFrac
• Circle U. 2023 seed-funding scheme
• European Research Council: ERC-2022-ADG grant agreement No 01096057 GLACMASS

Citation

@article{Nanni2025Observed,
  author = {Nanni, Ugo and Bouchayer, Coline and Åkesson, Henning and Lefeuvre, Pierre-Marie and Mannerfelt, Erik Schytt and Köhler, Andreas and Gagliardini, Olivier and Kohler, Jack and Schmidt, Louise Steffensen and Hult, John L. and Renard, François and Schuler, Thomas V.},
  title = {Observed positive feedback between surface ablation and crevasse formation drives glacier acceleration and potential surge},
  journal = {Nature Communications},
  year = {2025},
  doi = {10.1038/s41467-025-66349-9},
  url = {https://doi.org/10.1038/s41467-025-66349-9}
}