Greenland’s Hidden Mega-Canyon: 750 km Beneath the Ice Sheet

Under two kilometres of ice in the middle of Greenland lies a canyon at least 750 kilometres long and up to 800 metres deep. A team led by Professor Jonathan Bamber of the University of Bristol revealed it in the journal Science on 29 August 2013, using decades of airborne radar measurements. Nobody has ever seen it: the whole canyon is buried beneath the Greenland Ice Sheet.

A mega-canyon under the Greenland Ice Sheet

The paper, “Paleofluvial Mega-Canyon Beneath the Central Greenland Ice Sheet”, described a winding valley that runs from near the centre of the island to its northern edge, where it opens into a deep fjord connected to the Arctic Ocean. In depth and shape it compares with parts of the Grand Canyon in Arizona.

Bamber worked with Martin Siegert, Jennifer Griggs, Shawn Marshall and Giorgio Spada, with funding from the EU ice2sea programme and the UK’s Natural Environment Research Council.

How radar found the buried canyon

Ice is transparent to certain radio frequencies, so radar flown over an ice sheet can measure all the way to the rock beneath. The pulses travel down through the ice and bounce back from the bed, and the delay tells scientists how thick the ice is and how high the ground below lies.

The team combined thousands of kilometres of flight lines collected mainly by NASA and by British and German researchers over several decades, including NASA’s six-year Operation IceBridge airborne mission. Stitched together, the lines revealed a continuous meandering channel that no single flight could show. The 3D image above is a reconstruction of that bedrock surface.

NASA Goddard’s video shows the canyon emerging as the ice is stripped away digitally.

An ancient river older than the ice

The canyon’s meandering form looks like a river valley, and the researchers concluded that it is just that. It is thought to predate the ice sheet that has covered Greenland for the last few million years, and evidence suggests it carried water from the interior to the coast for at least four million years.

Today it still matters. The study suggests that the canyon channels meltwater produced at the base of the ice from the interior towards the northern margin and into the ocean, influencing how water moves beneath the ice sheet.

Greenland Ice Sheet facts

The canyon’s cover is the second-largest body of ice on Earth after Antarctica. According to the US National Snow and Ice Data Center:

• The ice sheet covers about 1.7 million square kilometres, roughly four-fifths of Greenland.
• It is more than 3 km thick at its thickest point.
• It holds about 2.9 million cubic kilometres of ice.
• If it all melted, global sea level would rise by about 7.4 metres.

Mapping the ground beneath it helps scientists model how the ice flows and how it will respond to a warming climate. As NASA IceBridge project scientist Michael Studinger put it, the find shows how little we still know about the bedrock below large continental ice sheets.

More on Greenland and polar ice

For the water you can see on the surface, read about Greenland’s visible meltwater channels, and for life beneath the ice in Antarctica, our research on a former subglacial lake.