What may have been the world's tallest waterfall briefly formed on Greenland's ice sheet last year, draining a meltwater lake of 5 million cubic meters of water -- equivalent to 2,000 Olympic-sized swimming pools -- in just five hours.
Scientists from the University of Cambridge in the UK recorded the extraordinary phenomenon through the use of aerial drones.
Their study, published this week
in the journal Proceedings of the National Academy of Sciences, investigates the link between this transfer of meltwater to the bottom of the ice and rising global sea levels. Greenland has the world's second-largest ice sheet, and is the single largest contributor to global sea-level rise, the study said.
"Before this study, we already knew that many lakes drain and that fractures may be important in the lake drainage process, but the formation of fractures in terms of 'where', 'when' and 'how' has not been studied before, at least not with the resolution and details featured in our work," one of the researchers, Poul Christoffersen, from Cambridge's Scott Polar Research Institute, who led the research told CNN via e-mail.
Caused by cracks forming on the ice sheet, these cascades are responsible for dumping huge quantities of surface water to the ice bed, where it can accelerate the movement of ice towards the sea. After draining, lakes leave behind holes called moulins, which allow meltwater to continue to travel to the bottom of the ice sheet.
"When trigger lakes drain, the water lubricates the bed and the ice flow becomes faster," Christoffersen said.
"Previously this acceleration was thought to be short-lived, and have little overall impact on the ice sheet, but we have shown that even localized and short-lived accelerations caused by the drainage of trigger lakes can open fractures and result in additional drainages of lakes in a more stable setting."
Formed during the summer as the weather warms, the 'trigger lakes' such as the one the scientists observed at Store Glacier, in northwest Greenland, can cause a chain-reaction so that up to 50 or more lakes nearby can drain rapidly over the course of a few days, Christoffersen said.
At its peak, the cascade was 950 cubic meters per second, which is roughly half of the flow of Niagara Falls or one Olympic sized swimming pool every three seconds, he said. The water was plunging "pretty much exactly" 1,000 meters (3,281 feet), said Christoffersen.
Angel Falls in Venezuela is the world's highest waterfall, standing at around 3,210 feet.
"This discharge increased the ice flow from two meters per day to five meters per day as the water delivery took place. This acceleration had a sudden impact on the ice sheet in terms of stress and ice deformation, and these dynamic impacts explain why lakes situated in places where fractures do not naturally form, still drain rapidly," said Christoffersen.
The team used GPS-fitted, autonomous drones to take about 900 photographs of the lake's disappearance.
The photographs were stitched together and made into 3D surface elevation models, Christoffersen said.
Christoffersen said climate change plays a key role in the increase of meltwater production, as global temperatures rise.
"More and more melt water is being produced and melting extends to higher and higher elevations," he said. "Lakes are growing larger and more numerous and forming at higher elevations. Some as high as 2 kilometers above sea level. This means that networks of lakes draining in cascading events are likely to grow larger."
"It's possible we've under-estimated the effects of these glaciers on the overall instability of the Greenland Ice Sheet," said 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."
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