A new study, led by the Lancaster University and involving the Alfred Wegener Institute, reveals how, under extreme conditions, melt water flooding underneath the ice can force its way upwards through the ice and escape at the ice sheet surface. Researchers observed this phenomenon for the first time in Greenland and described it in detail in the journal Nature Geoscience. It sheds new light on the destructive potential of meltwater stored beneath the ice sheet.
The international team of researchers studied a previously undetected lake beneath the ice sheet (known as a subglacial lake) in a remote region of northern Greenland, using state-of-the-art satellite data and numerical models. Using detailed three-dimensional representations of the ice sheet surface from the ArcticDEM project, alongside data from a number of European Space Agency (ESA) and NASA satellite missions, they monitored the sudden drainage of this lake.
![[Translate to English:] 3D-Perspektive der Bruchzone, aus der das Schmelzwasser austrat, basierend auf Satellitenbildern vom 28. April 2015. Die Bruchzone erstreckt sich über eine Fläche von etwa 54 Fußballfeldern (385.000 Quadratmeter).](/fileadmin/user_upload/AWI/Ueber_uns/Service/Presse/2025/3_Quartal/OM_Schmelzwasser_Flut_Gr%C3%B6nland_Eis/6_fracture_zone_3d.jpg "[Translate to English:] 3D-Perspektive der Bruchzone, aus der das Schmelzwasser austrat, basierend auf Satellitenbildern vom 28. April 2015. Die Bruchzone erstreckt sich über eine Fläche von etwa 54 Fußballfeldern (385.000 Quadratmeter).")
The researchers discovered that over a period of 10 days in summer 2014, an 85 metre-deep crater appeared across a 2 km2 area in the ice surface, as 90 million cubic metres of water flooded out of the underlying lake. This roughly equates to nine hours of water gushing over the Niagara Falls during its peak season, and represents one of the largest Greenland subglacial floods in recorded history.
However, what the researchers found further downstream was even more surprising: In a region of previously unblemished ice, they observed the sudden appearance of an area the size of around 54 football pitches (385,000 square metres) of fractured and distorted ice; comprising deep cracks and 25 m high uprooted ice blocks, together with a freshly water-scoured ice surface. “For this to happen, cracks have to develop diagonally through the ice to the surface,” says Prof Angelika Humbert, glaciologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). These cracks create a path through which the water can then flow upwards. “Even if this seems unusual at first, such cracks are well known in fracture mechanics.”
Lead author Dr Jade Bowling, who led this work as part of her PhD at Lancaster University, said: “When we first saw this, because it was so unexpected, we thought there was an issue with our data. However, as we went deeper into our analysis, it became clear that what we were observing was the aftermath of a huge flood of water escaping from underneath the ice.”
Although it had been previously assumed that meltwater flows from the surface to the base of the ice sheet, and then onwards to the ocean, this research provides clear evidence that water can also travel upwards, in the opposite direction. It also surprised the scientists to find that the flood occurred in a region where models predicted that the ice was frozen at the bed, leading the researchers to propose a mechanism whereby pressure-driven fracturing of ice along the ice bed created a pathway for the water to then flow.
As such, these discoveries highlight the complexity of water flow, and the need to better understand how the ice sheet responds to extreme inputs of meltwater; something which is likely to become more common as our climate warms, and surface melting intensifies and expands into new areas.
Original publication
Bowling, J.S., McMillan, M., Leeson, A.A. et al. Outburst of a subglacial flood from the surface of the Greenland Ice Sheet. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01746-9