Lakes forming next to Greenland’s melting ice sheet are speeding up glacier flow

A growing network of meltwater lakes at the edge of the Greenland ice sheet is accelerating the flow of major glaciers, potentially increasing the pace of global sea‑level rise.

Warmer air and sea temperatures have led to the loss of around 264 gigatons of ice every year in Greenland since 2002 causing sea levels to rise by 0.8 millimetres annually. But a new study by the University of Leeds examining glacier behaviour across the entire ice sheet has highlighted a lesser‑known feature that is amplifying this mass loss - the freshwater lakes forming as the ice retreats. 

These ice-marginal lakes (or IMLs) sit right up against the edge of the ice and appear as glaciers pull back and expose deep, bowl‑shaped hollows in the landscape. Meltwater quickly pools in these basins to form lakes as large as 117 km2 in area.   

By showing that lakes at the ice margin can substantially speed up glaciers, we identify an important process that needs to be included in predictions of future ice loss.

The study which is published today in the journal Communications Earth and Environment shows that far from being passive features of the landscape, the lakes can destabilise the glaciers that feed into them, triggering movement, increasing thinning, and heightening ice loss. 

The researchers examined satellite data, using maps of ice-marginal lakes across Greenland and the flow at the ice sheet surface. They found that the speed of glaciers ending in lakes was over three times faster at their fronts than those glaciers ending on land. Crucially, that acceleration wasn’t confined to the glacier edge, with the effect being detected up to 3.5 km inland. 

Lead author of the study Connie Harpur, a post-graduate researcher in Leeds’ School of Geography, said: “Our findings are significant because glacier speed plays a major role in how quickly ice is lost from the Greenland Ice Sheet. When glaciers flow faster, they deliver more ice to lower elevations, where it can melt, or to their fronts, where it can break away.  

“By showing that lakes at the ice margin can substantially speed up glaciers, we identify an important process that needs to be included in predictions of future ice loss.” 

Ice retreat

Around 10% of Greenland’s ice edge is currently bordered by freshwater lakes with that figure expected to rise sharply as the climate warms and more depressions are exposed during ice retreat.  

Much like glaciers that flow into the ocean, those ending in lakes can experience a form of flotation, where the water partly lifts the glacier front, increasing melting under the ice. This makes it easier for large slabs of ice to break off in a process known as calving and reduces the friction that usually slows the glacier’s flow. 

Earlier observations from mountain ranges such as the Himalayas have shown that glaciers terminating in lakes can move twice as fast as nearby glaciers ending on land. But until now, scientists had only limited evidence of how widespread these effects might be in Greenland. 

The Leeds researchers warn that this omission could be significant. Ice dynamics (the ways in which glaciers speed up, slow down, and deform) are expected to be the main driver of Greenland’s ice loss in the coming decades and with lake formation accelerating alongside climate warming, the study’s authors argue that models urgently need to account for the role of IMLs. 

Co-author of the study Professor Mark Smith added: “If we do not account for lake effects, we may underestimate how dynamically parts of the ice sheet respond to future warming, and in turn how much Greenland will contribute to future sea level rise. 

“Understanding ice-marginal lakes’ influence on glacier flow is crucial for accurate projections.” 

Further information

Top image: An ice-marginal lake in southwest Greenland. Photo credit – Connie Harpur. 

Ice-marginal proglacial lakes enhance outlet glacier velocities across Greenland is published in Communications Earth and Environment.

For media enquiries, please contact Kersti Mitchell via k.mitchell@leeds.ac.uk