In the remote expanses of Greenland’s vast ice sheet, a striking and increasingly concerning phenomenon has been unfolding over the past few decades. Since 1995, a large meltwater lake—situated on the surface of the 79-degree North Glacier—has emerged and evolved, drastically altering the dynamics and structural integrity of this crucial glacial mass. Scientists, led by Prof. Angelika Humbert from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), have been meticulously observing this lake and the pronounced geological responses it has incited within the glacier’s ice.
The lake had no prior existence before the mid-1990s, its formation coinciding with a marked rise in atmospheric temperatures attributed to accelerating climate change. Over the near three decades since its formation, the surface water body has undergone episodic and abrupt drainage events, whereby vast volumes of freshwater are rapidly discharged through an intricate network of fractures and subglacial pathways. These remarkable drainages—totaling seven major events since 1995, with four occurring within the last five years alone—have introduced significant mechanical stresses to the glacial ice, ultimately lifting and reshaping the glacier’s structure.
What makes this superglacial lake particularly notable, as highlighted by Humbert and her team, is the development of unique triangular fracture fields that began to form from 2019 onwards. These fractures differ distinctly from previously observed meltwater drainage features. Characterized by their sharp, angular shapes and extensive size, these cracks have given rise to large channels called moulins, some measuring several dozen metres in width. Moulins serve as conduits transporting water rapidly through the ice, delivering massive pulses of meltwater directly to the glacier’s base, often within mere hours of the initial surface drainage.
The mechanics governing these fracture systems are a complex interplay of viscoelastic ice behavior. The ice sheet itself embodies a duality; it behaves simultaneously as a viscous fluid that deforms and flows on geological timescales, and as an elastic solid capable of deforming and recovering its shape much like a rubber band. This elastic characteristic facilitates the formation of cracks and channels within the ice, whereas its viscous flows contribute to the gradual closure and healing of these structures after drainage events. Radar imaging reveals that while surface fractures remain visibly stable over years, internal changes continue to occur, and a vast network of channels beneath the glacier allows water multiple escape pathways.
Intriguingly, the increasing frequency and intensity of these drainage events suggest a progressive modification of the glacier’s internal structure. The repeated reactivation of the triangular moulins appears to be a significant factor driving the shortening intervals between water discharge episodes. Rather than a static system, the glacier shows signs of dynamic evolution, constantly responding to meltwater influxes and the physical forces generated as water pressures fluctuate beneath the ice. This dynamism raises profound questions about the glacier’s resilience and its ability to revert to a “normal” winter state, where surface meltwater is less prevalent.
A compelling feature noted by the AWI researchers concerns the vertical displacement of the glacier’s ice along the fracture surfaces. High-resolution aerial photography has documented shadows cast by these cracks, indicative of ice blocks shifting upwards unevenly on either side of a moulin. At the location of the lake itself, radar surveys have detected subglacial lake formations—“blisters”—that exert upward pressure, effectively lifting parts of the glacier. Such phenomena underline that the meltwater does not merely exit the glacier passively but actively alters the ice sheet’s morphology and potentially its movement dynamics.
To rigorously analyze these developments, the research team has employed a combination of advanced remote sensing technologies, including satellite-based observations and airborne radar surveys. These data sources, integrated with viscoelastic modeling techniques, allow scientists to visualize not only the surface meltwater processes but also the complex internal hydrological and mechanical responses of the glacier. Understanding the formation, evolution, and closure of cracks and moulins is essential for predicting how meltwater influences glacier flow rates and overall ice mass balance, with direct implications for global sea level rise projections.
Furthermore, this research underscores the significance of incorporating fracture dynamics into modern ice sheet models. Traditionally, models have treated glaciers as uniform masses, often neglecting the intricate passageways meltwater constructs within the ice. The new findings from the 79°N Glacier emphasize that fractures and englacial channel networks significantly mediate meltwater drainage, altering the stress regime and potentially accelerating ice loss. Collaborative efforts between AWI, TU Darmstadt, and the University of Stuttgart are focused on refining these models to more accurately reflect observed meltwater drainage behaviors.
The continual rise in atmospheric temperatures and consequent increase in meltwater production elevate the urgency of this research. Notably, the fracture zones associated with the triangular moulins have been migrating upslope, expanding the area of the glacier susceptible to ice fracturing and meltwater infiltration. This upslope progression signals that the glacier’s structural changes may soon affect regions previously untouched by such stressors, potentially destabilizing larger sections of the ice sheet.
In essence, the 79°N Glacier represents a microcosm of the broader challenges facing ice sheets globally under climate warming scenarios. The multidisciplinary work spearheaded by Prof. Humbert and her colleagues reveals that supraglacial lakes and their associated drainage features are not benign surface events but are intricately linked to internal ice sheet dynamics with far-reaching consequences. These insights are critical as the scientific community endeavors to forecast the future of polar ice masses and their contributions to global sea level rise.
Despite the intense focus on this rapidly evolving glacial environment, fundamental questions remain unresolved. Key among them is whether the glacier’s drainage network is approaching a tipping point beyond which it cannot revert to historical patterns of stability. The recurring nature of these massive drainage episodes over mere hours to days presents an extreme hydrological disturbance, whose effects on glacier flow and stability are still poorly understood. Future research will need to quantify these feedback mechanisms to improve predictive capabilities.
By bridging observational data and sophisticated modeling, this study not only advances glaciological knowledge but also underscores the critical importance of considering meltwater-induced fracturing in climate change assessments. As meltwater continues to reshape ice sheets from above and below, understanding these processes is pivotal for society’s preparedness to cope with evolving cryospheric and sea-level change risks.
Subject of Research: Dynamics of supraglacial lake drainage, formation of triangular fractures, and englacial meltwater pathways in the 79°N Glacier, Greenland.
Article Title: Insights into supraglacial lake drainage dynamics: triangular fracture formation, reactivation and long-lasting englacial features
News Publication Date: 14-Aug-2025
Web References: https://doi.org/10.5194/tc-19-3009-2025
References: Humbert, A., Helm, V., Zeising, O., Neckel, N., Braun, M. H., Khan, S. A., Rückamp, M., Steeb, H., Sohn, J., Bohnen, M., and Müller, R.: Insights into supraglacial lake drainage dynamics: triangular fracture formation, reactivation and long-lasting englacial features, The Cryosphere, 19, 3009–3032, 2025.
Image Credits: Alfred-Wegener-Institut
Keywords: Glaciers, Climate change, Ice melt
