Two Greenland lagoons drain away in weeks
A team of researchers, building the highest-resolution map of the Greenland Ice Sheet, has made the surprising discovery of billions of gallons of water being drained away in a matter of weeks from sub-glacial lakes leaving miles-wide empty craters.
They discovered two lakes of meltwater that pooled beneath the ice and rapidly drained away, due to mysterious natural drainage tunnels extending inland from the coast.
One of the lakes has filled and emptied twice in the last two years, according to researchers at Ohio State University and Cornell University in Ithaca, New York, who published their findings in the journals Nature and The Cryosphere.
Ian Howat, associate professor of earth sciences at Ohio State university, believes that the finds add to a growing body of evidence that meltwater has started overflowing the ice sheet's natural plumbing system and is causing 'blowouts' that drain lakes away.
'The fact that our lake appears to have been stable for at least several decades and then drained in a matter of weeks - or less - after a few very hot summers, may signal a fundamental change happening in the ice sheet,' Professor Howat said.
Another lake, measuring 3km was discovered by a team from Cornell University.
Using Nasa data, they calculated that the lake has filled and emptied twice since 2012 – at one point, experiencing a 'blowout' that drove water from the lake at a volume of 57,000 gallons (215 cubic metres) which is the equivalent to a 30 by 50 ft swimming pool, every second.
Co-author of the study, Michael Bevis, said that this repeated filling and refilling is troubling.
Each time the lake fills, the meltwater carried stored heat along with it, which reduces the stiffness of the surrounding ice, making it more likely to flow out to sea, he explained.
'If enough water is pouring down into the Greenland Ice Sheet for us to see the same sub-glacial lake empty and re-fill itself over and over, then there must be so much latent heat being released under the ice that we'd have to expect it to change the large-scale behaviour of the ice sheet,' he said.
Professor Howat's team came across a cratered lake last year, which is 31 miles (50km) inland from the southweat Greenland coast. It measures 1.2 miles (2km) across and 230 feet (70 metres) deep.
Aerial and satellite images revealed that a sub-glacial lake had existed at the site for more than 40 years, while recent images suggested that it probably emptied through a meltwater tunnel beneath the ice sheet in 2011.
The lake would have held around 6.7 billion gallons of water, but disappeared in a single season, with Professor Howat describing the sudden drainage as 'catastrophic'.
He suspects that as more meltwater reaches the base of the ice sheet, natural drainage tunnels along the coast are cutting further inland.
The tunnels carry heat and water to areas that were once frozen to the bedrock, potentially causing the ice to melt faster.
He explained: 'Some independent work says that the drainage system has recently expanded to about 50 kilometres inland of the ice edge, which is exactly where this lake is.'
It is possible that the lake was tapped by one of the invading tunnels and that thousands of similar lakes dot Greenland's coast.
Researchers are not entirely sure how the lakes, which are hard to detect with radar, form and know relatively little about what is happening under the ice in the region.
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