The Greenland Ice Sheet may be even more unstable than scientists previously thought, according to new research that reveals how lakes on the surface of Greenland's glaciers drain toward the bottom of the ice sheet within hours.
An impressive new time-lapse video shows one of these vanishing acts on Store Glacier in western Greenland. In July 2018, the lake lost two-thirds of its volume in a mere 5 hours, gushing out the equivalent of 2,000 Olympic-size swimming pools. Even after the lake finished draining, the fracture that emptied it remained, leaving an easy conduit from the surface of the glacier to its base just over a half-mile (1 kilometer) below.
"Every year, there are many hundreds of large waterfalls providing water, but also large quantities of energy, down to the base of the ice sheet," said Poul Christoffersen, a glaciologist at the University of Cambridge's Scott Polar Research Institute. This water lubricates the bottom of the ice sheet, hastening its movement toward the sea, where it can contribute to sea level rise.
Since satellite observation of the island began in the 1970s, the number of meltwater lakes dotting Greenland's ice has risen. These seasonal lakes have also started growing larger, and appearing at higher elevations, than in the past. These trends are linked with a general warming trend in Greenland, which has been experiencing high rates of melt as the globe warms.
Meltwater lakes are a part of this story, but they've been underestimated, Christoffersen told Live Science. Between a quarter and almost a half of these lakes experience rapid draining that sends their water deep into the ice, but satellite observations don't capture these draining events very precisely. Researchers have also tended to see the lake losses as local phenomena, Christoffersen said, not events that affect the larger movements of the ice sheet.
But Christoffersen and his team have evidence that suggests these lakes do matter — a lot. In May 2018, the researchers published a paper in the journal Nature Communications revealing that lakes tend to drain in clusters. The drainage of one lake can cause the ice surface to crack and fracture further, triggering other lakes to drain as well. The fractures left behind also act as conduits for further meltwater drainage, creating kilometer-tall waterfalls plunging into the ice.
"You actually have quite a big effect," Christoffersen said.
On July 7, 2018, Christoffersen and his team were camped out near a meltwater lake called Lake 028 on Store Glacier when they noticed that the lake level was dropping fast.
"We could see a fracture that formed in the ice, and water was gushing into this fracture as it opened up," Christoffersen said.
Luckily, Scott Polar Research Institute doctoral candidate Thomas Chudley was at the scene with an aerial drone he'd been using to capture imagery of the glacial surface close-up. Chudley flew the drone over the lake at regular intervals as it drained, securing a detailed look at how the drainage occurred. The researchers published their findings Dec. 2 in the journal Proceedings of the National Academy of Sciences.
One major lesson from the loss of Lake 028 was that though the lake didn't disappear completely, it still drained rapidly toward the base of the ice sheet, Christoffersen said. In satellite studies, researchers have largely ignored partial lake drainages, he said; the assumption has been that partial drainages occur when lake water flows out of the lake basin across the surface of the ice, where it isn't likely to have much effect on overall ice sheet movements.
The new observations suggest that this assumption is wrong. The lake's drainage sent more than 1.26 billion gallons (4.77 billion liters) of water toward the base of the ice, where it can do the most damage. The only reason the lake didn't drain completely was that the fracture didn't extend into the deepest part of the lake basin.
"That means that, in hindsight, we've been underestimating the ability of lakes to drain and create conduits that transfer water from the surface to the base of the ice sheet," Christoffersen said. The data from this research can be used to improve computer simulations that predict what the ice sheet will do in the future, he said.
"Understanding exactly how these fractures intersect lakes and how the lakes subsequently interconnect is going to play a key role in how we will model the ice sheet in a much more refined and realistic way in the future," Christoffersen said.
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Originally published on Live Science.