Greenland is becoming unstable as lakes empty into the bottom of the ice sheets: study
Greenland’s ice sheet — the world’s second-largest expanse of ice, measuring three times the size of Texas — is melting at an alarming pace, with the island already contributing to about 25% of the global sea-level rise. Making matters worse are cracks splitting the ice sheet. It is through these cracks that Greenland’s lakes empty into the bottom of the ice sheet, making the island (pictured above — image courtesy of Thomas R. Chudley) increasingly unstable, suggests drone records of the faltering ice sheet.
These lakes are formed during summers, as the ice begins to melt, resulting in “supraglacial” lakes forming on the surface of the ice. Many of these lakes drain through the cracks and crevasses in the ice sheet.
When one lake pours into the crack, the water quickly spreads under the ice sheet. This could, in turn, open new cracks on the surface, leading to more lakes emptying into the cracks, setting off a chain reaction.
"It's possible we've underestimated the effects of these glaciers on the overall instability of the Greenland Ice Sheet," says co-first author Tom Chudley, a PhD student at the Scott Polar Research and the team's drone pilot. "It's a rare thing to actually observe these fast-draining lakes — we were lucky to be in the right place at the right time."
From the drone images, the team showed how the melting ice or snow could create new cracks and activate dormant cracks. In one such observation, they saw that in just five hours, five million cubic metres of water — the equivalent of 2,000 Olympic-sized swimming pools — drained to the bottom of the ice sheet through the crack, reducing the lake to a third of its original volume. The whole process could lift the ice sheet by half a metre.
"To date, most observations are provided by satellites. These allow us to see what's happening over the whole ice sheet, but drone-based observations give a lot more nuance to our understanding of these lake drainages. We can also observe the formation and re-opening of fractures, which isn't possible from satellites," says Dr Poul Christoffersen who led the research.
After recording how cracks contribute to drainage of lakes, the team is now interested in identifying 'hotspots' where the ice sheet behaves sensitively. The team will also explore how the ice sheet may change over the coming decades as the climate continues to warm.
The study has been published in the Proceedings of the National Academy of Sciences.