Vast canyon discovered under Greenland ice sheet

Earth 29 August 2013

Video: Fly through the canyon

A 3-D view of the hidden canyon
A 3-D view of the hidden canyon

(Image: J. Bamber, University Bristol)

Hidden beneath the thick layers of ice that smother Greenland, there is a valley to rival the Grand Canyon. At almost twice the length of Arizona’s landmark, the canyon once carried a river as large as any in Europe, until it was buried by the encroaching ice 3.5 million years ago.


Greenland is home to one of Earth’s two major ice sheets, the other being in Antarctica. The ice, several kilometres thick, conceals the underlying landscape so, until recently, we did not know much about Greenland’s rocks. However, ice-penetrating radar scanners, flown over the ice sheet by aircraft, can reveal the shape of the ground.

By 2001, glaciologists had built up a three-dimensional picture of Greenland’s bedrock, but the resolution was fairly poor so many features were invisible, says Jonathan Bamber of the University of Bristol, UK. “Since then, NASA has been flying airborne campaigns every season. We’ve got a much denser network of measurements.”

In the radar images, Bamber and colleagues immediately spotted a massive canyon. It stretches for at least 750 kilometres, running from the centre of the island to its northern coast. That is almost twice as long as the Grand Canyon, which runs for 446 km.

Big river

“It’s a huge feature,” says Bamber. “It’s not every day, or even every decade, that one discovers a relict river almost twice the length of the Grand Canyon.”

In the south, where it begins in the hills, the canyon is about 200 metres deep, but as it runs north it deepens to 800 m. For much of its length it is 10 km wide. On these measures, the Grand Canyon is considerably bigger: parts of it are 1.6 km deep.

Bamber says that the hidden canyon helps to explain why Greenland does not have any lakes trapped under its ice sheet. In Antarctica such lakes are common: Lake Vostok is the most famous, but there are over 100, many of them connected in a plumbing network that spans the continent. No such lakes have been found under the Greenland ice and the hidden canyon may be partly responsible: meltwater would swiftly run down it and into the sea.

The mega-canyon also helps explain why the base of Greenland’s ice sheet is not particularly slippery. The slipperiness helps determine how quickly the ice sheet will slide into the sea as the climate warms – and thus how quickly sea levels will rise. When parts of the ice melt, liquid water trickles to the base and this can lubricate the underside of the ice sheet, allowing it to slide more quickly into the sea and drive up sea levels at a faster rate. For this to happen, the water must spread out in a thin film across a large area. But in Greenland this doesn’t happen much because the water drains away through big channels like the mega-canyon. “This huge channel means that a lot of the water being generated in north Greenland is not having a big impact on [ice] flow,” says Bamber.

The improved radar data means we are unlikely to find any more such surprises lurking under Greenland’s ice. “This is the largest feature we’re ever gonna discover under Greenland,” says Bamber.

However, Antarctica is a different story. It is 10 times the size of Greenland and some parts are still poorly mapped. “It’s possible that there is something similar under Antarctica,” says Bamber. Already, remote sensing is revealing the detailed shape of an alpine mountain range hidden beneath the southern ice cap.

Journal reference: Science, DOI: 10.1126/science.1239794

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