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Summer meltwater has drained through a snow-covered channel in Greenland.

Summer meltwater has drained through a snow-covered channel in Greenland. Scientists say that the Greenland Ice Sheet sits atop a canyon twice as long as the Grand Canyon.

Photograph by James Balog, National Geographic

Jaclyn Skurie

National Geographic

Published August 29, 2013

Imagine if you could pick up the Greenland Ice Sheet and see what lies beneath. Surely 1.7 million square kilometers of slowly thawing ice must rest on a massive pool of melted water, right?

Not necessarily, according to a study released today in the journal Science. Unlike the ice sheet covering Antarctica that sits atop numerous lakes, the Greenland Ice Sheet blankets a giant subglacial canyon nearly twice as long as the Grand Canyon located in Arizona. (Read: "Changing Greenland" in National Geographic magazine.)

Scientists suggest the canyon—which runs as deep as half a mile (800 meters) and as long as 466 miles (750 kilometers)—is paleofluvial, meaning it originated as a system of rivers in Greenland's hard bedrock surface. According to this research, the canyon is part of an organized valley system that carries meltwater away from the inland ice sheet and funnels it toward coastal fjords connecting to the Arctic Ocean. (Related: "Ancient Global Warming Raised Sea Levels Nearly 70 Feet.")

Jonathan Bamber, lead author of the study and a physical geography professor at the University of Bristol in the United Kingdom, says he believes the canyon pre-dates the ice sheet. Before the land was completely glaciated at least four million years ago, melt from partial ice cover likely flowed through the bedrock canyon.

Since then, the features of the land have survived glaciation without significant erosion.

Beyond the Surface

While flying over the ice sheet, scientists over the past three decades have measured the depths of the canyon using a radar system that operates at frequencies where ice is transparent to radio waves—from around 50 megahertz to 500 megahertz. A pulse of energy is sent down to penetrate through the ice, bounce off the bedrock, and travel back to the radar system. (Also read: "'Shocking' Greenland Ice Melt: Global Warming or Just Heat Wave?")

Bamber and his team compiled this decades-worth of airborne radar data, mainly from NASA, to build a more comprehensive picture of what sits under the Greenland Ice Sheet.

The data have made him curious about other parts of the world. The Antarctic Ice Sheet, which is ten times as large as Greenland's, sits on a complex topography that includes bedrock and mountain ranges. After the recent canyon discovery in Greenland, Bamber says it is hard not to wonder about the areas of Antarctica still left to be explored.

Greenland has been glaciated for about 3.5 million years, and will continue to remain so for thousands more. But because of constantly increasingly global temperatures, it is difficult to determine when exactly the glacial land ice will completely erode. Understanding what happens to meltwater will be crucial for research on the future of glacial melt and rising sea levels. (Watch: "Greenland Ice Sheet.")

"If we carry on warming up the planet, the ice is going to melt faster than we want it to," Bamber said. "It really depends on what we do to the planet, doesn't it?"

Follow Jaclyn Skurie on Twitter.

Cahya Nugraha
Cahya Nugraha

however, we must care to our world. action is more better than only speak..

nice artice :)

Graham Darling
Graham Darling

"radar system that operates at frequencies transparent to radio waves" should be "radar system that operates at frequencies where ice is transparent transparent to radio waves", or something like that

Donald Mcclure
Donald Mcclure

" But because of constantly increasingly global temperatures" Ahem- for the last 16 years no rise in global temperatures confirmed by the proponents of taking civilization back to the stone age to preserve the planet. Can anyone at NG explain why you allow a comment that is not factual to be published without noting the 16 year fact????

craig hill
craig hill

The end of this article is typical mushy toothless gummy Nat Geo "My Weekly Reader" for chronological adults.  It's not a matter of the ice melting unless we someday get around to do something about it, that's already in the pipeline of the indolence we're so great at right now.  It's a fait accompli. The methane roaring out of the permafrost in the Arctic surrounding Greenland has already upticked the equivalent CO2 meter to 465 parts per million, which is far greater than we're being told (thanks, Nat Geo, for helping keep us dumb), which insures, via numerous feedback loops never addressed in media, in a 4 degree celcius rise by the 2040s, which is not survivable, among many other deadly consequences from sitting on our couches watching and reading happy human interest tales from Nat Geo.

We are past the tipping point.  It's over, ignorant humans.   

Cheryl Parker
Cheryl Parker

Interesting topic, but I don't think that's a picture of Greenland. Those are the Delbridge Islands in Antarctica right? :)

Libor Zicha
Libor Zicha

I'm not aware of Erebus Glacier Tongue in Greenland. But there is one for sure in Antarctica.

Todd Brown
Todd Brown

@Donald Mcclure  Please reference your data source, I suspect you are just using a data set that has been cherry picked.  Also no one is proposing going back to the Stone Age level of technology, OK maybe the crackpot fringe is, but your hyperbole doesn't help foster a rational debate.

Do me a favor and look at the last 30 + years of NASA satellite pictures of the Arctic Ocean Ice Cap and then with a straight face try to say the cap isn't shrinking. And don't just try to hide behind finding two data points that do not fit the trend as a way to discount the entire data set.

Daniel Newman
Daniel Newman

@craig hill 

Yeah, numerous feedback loops that are computer models that have no credibility.  LOL.  The wildfire in California is blowing more CO2 into the air than all of California vehicles for a full year.  Your arrogant post is misinformed.  Incidentally, the permafrost region of the Arctic has lots of plant life that breathes O2 into the air from all that dirty CO2. Of course, that's just not in the model, is it?

Jaclyn Skurie
Jaclyn Skurie

Hi @Cheryl Parker @Libor Zicha: 

Thanks for the catch! I am the author of this article—just an update that the photo and caption have been changed to reflect the content. 

Daniel Newman
Daniel Newman

@Todd Brown @Donald Mcclure 

You do know about Antarctic ice don't you?  It's been at record levels for all year. Never before so much ice there in the historical record.  How does this fit in with global warming?  Seems like Antarctica ice growth is balancing Arctic ice loss.  Maybe the so called global warming is actually local warming in the N hemisphere because of local conditions.


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