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article imageFast-draining lakes pose a new risk for Greenland ice sheet

By Karen Graham     Mar 16, 2018 in Science
A growing number of lakes on the Greenland ice sheet are causing a runaway chain reaction to take place under the ice and it could possibly lead to its collapse.
Researchers from the UK, Norway, U.S., and Sweden have used a combination of 3D ice-flow models and satellite images, as well as real-world observations to show how a growing network of lakes on the Greenland ice sheet has been found to drain in a chain reaction that speeds up the flow of the ice sheet, threatening its stability.
It is almost surreal, but imagine actually seeing a 2.2-square-mile (5.6 square kilometers) lake containing 11.6 million gallons of melted ice drained away into nothing in less than 2 hours. Glaciologists saw this happen in 2006.
Scientists who witnessed the event said the water gushed all the way down to the bed of the ice sheet, through almost 0.6 miles (1 kilometer) of ice. The flood doubled the average speed of the ice sheet's slide across the bedrock underneath it.
Thousands of supraglacial lakes form on top of the Greenland ice sheet each summer  with some of the...
Thousands of supraglacial lakes form on top of the Greenland ice sheet each summer, with some of them being miles wide.
Woods Hole Oceanographic Institution
Supraglacial or ice-melt lakes form on the surface of the Greenland ice sheet each summer as the weather warms, and quite often, can hang around for weeks or months. But when they drain quickly they transfer huge quantities of heated water to the base of the ice sheet.
A runaway chain reaction
According to a new paper published in the journal Nature Communication on March 14, 2018, the research team found that the supraglacial lakes are starting to drain farther and farther inland, causing a "cascading chain reaction" enabled by a vast, interconnected web of cracks below the ice. And as the climate gets warmer, the web is getting wider.
The network of "melt lakes" reaches as far as 135 kilometers (83.9 miles) inland, according to the study – a distance previously thought to be impossible. They also reach elevations as high as 2,000 meters (6,562 feet).
The images above were acquired on July 15  2015  by the Operational Land Imager (OLI) on Landsat 8. ...
The images above were acquired on July 15, 2015, by the Operational Land Imager (OLI) on Landsat 8. They show meltwater lakes on the ice near Greenland’s west coast, about 100 kilometers (60 miles) southeast of Ilulissat.
NASA
Twenty-five years ago, the Greenland ice sheet, which covers 1.7 million square kilometers [656,374 square miles] was considered to be fairly stable, says Poul Christoffersen, a team member from the University of Cambridge. "But it now loses one billion tonnes of ice every day," he adds.
"This causes one millimeter [0.04 inches] of global sea level rise per year, a rate which is much faster than what was predicted only a few years ago."
"Lakes that drain in one area produce fractures that cause more lakes to drain somewhere elsewhere," co-author Marion Bougamont, a glaciologist at the University of Cambridge's Scott Polar Research Institute, said in a statement. "It all adds up when you look at the pathways of water underneath the ice."
Greenland s lakes are draining away in hours  thanks to a vast network of fissures hidden on the ice...
Greenland's lakes are draining away in hours, thanks to a vast network of fissures hidden on the ice sheet below.
Woods Hole Oceanographic Institute.
Cascading effect taking place
The draining of supraglacial lakes have previously been thought to be isolated events, but the new research shows the lakes form a massive network that is increasingly becoming interconnected as the temperature warms.
When one lake drains, the water quickly spreads under the ice sheet, which responds by flowing faster. The faster flow opens new fractures on the surface and these fractures act as conduits for the drainage of other lakes, according to the researchers.
This chain reaction becomes a cascading event, like an undulating row of dominoes toppling over, one after another, and can temporarily accelerate the ice flow by as much as 400 percent, making it less stable and at the same time affecting the degree of sea level rise.
The Greenland ice sheet lost close to two trillion tonnes of ice mass between 2003 and 2013
The Greenland ice sheet lost close to two trillion tonnes of ice mass between 2003 and 2013
Jeremy Harbeck, NASA Goddard/AFP/File
Basically, the study suggests that meltwater delivered to the base of the ice sheet through draining lakes drives episodes of sustained acceleration extending much farther into the interior of the ice sheet than previously thought.
“Transfer of water and heat from the surface to the bed can escalate extremely rapidly due to a chain reaction,” said Christoffersen. “In one case we found all but one of 59 observed lakes drained in a single cascading event. Most of the melt lakes drain in this dynamic way.”
What does all this mean? Climate change is altering the environment, and this is one more reason we really need to take this and other studies seriously. We must reduce greenhouse gas emissions and prepare our coastal cities for the impacts of sea level rise.
More about Greenland, Antarctica ice sheet, drainage events, Fractures, computer modeling