Over a 10-day period in the summer of 2014, a massive crater – 85 metres deep and spanning 2 square kilometres – formed on the surface of the ice sheet as 90 million cubic metres of water were suddenly released from this hidden subglacial lake.

This is equivalent to about nine hours' worth of water thundering over Niagara Falls at peak flow, making it one of the largest recorded subglacial floods in Greenland.

While the sudden surge of meltwater was startling in itself, even more alarming was the accompanying damage – towering 25-metre-high ice blocks torn from the surface, deep fractures in the ice sheet, and the ice surface scoured by the flood’s destructive force.

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.
Even more unexpected was the discovery that the flood took place in an area where models had indicated that the ice bed was frozen. This led researchers to suggest that intense pressure caused fractures beneath and through the ice sheet, creating channels through which the water could rise.

Current models that predict how ice sheets will respond to climate change and increased melting do not account for these upward-flowing, fracture-driven processes.

Mal McMillan, Co-Director of the Centre of Excellence in Environmental Data Science at Lancaster University, and Co-Director of Science at the UK Centre for Polar Observation and Modelling, said, “This research demonstrates the unique value of long-term satellite measurements of Earth’s polar ice sheets, which – due to their vast size – would otherwise be impossible to monitor.
“Satellites represent an essential tool for monitoring the impacts of climate change, and provide critical information to build realistic models of how our planet may change in the future.

Over 385,000 square meters, about the size of 54 football fields, was covered in deep crevasses and towering, 25-meter-high upturned ice blocks.

Surrounding this zone was another six square kilometers of scoured terrain, nearly twice the size of New York’s Central Park.

The scale and violence of the flood left researchers with little doubt about the power of water moving beneath the ice.

Until now, most models of Greenland’s ice sheet assumed that meltwater moves from the surface down through the ice, eventually draining into the ocean.

This study shows that, under extreme pressure, subglacial water can move in the opposite direction, fracturing the ice from below and exploding upward.

Because most models don’t include these mechanisms, they may be underestimating the ice sheet’s vulnerability.

Even more surprisingly, the flood occurred in a region where the bed of the ice sheet was thought to be frozen solid.

That led researchers to propose a new mechanism: extreme water pressure caused fracturing along the ice base, which in turn allowed the water to erupt through the ice and escape at the surface.