GSFC: Mega-Canyon under Greenland Ice Sheet

[bystander]

NASA Data Reveals Mega-Canyon under Greenland Ice Sheet
NASA | Goddard Space Flight Center | Operation IceBridge | 2013 Aug 29

Click to play embedded YouTube video.

Data from a NASA airborne science mission reveals evidence of a large and previously unknown canyon hidden under a mile of Greenland ice.

The canyon has the characteristics of a winding river channel and is at least 460 miles (750 kilometers) long, making it longer than the Grand Canyon. In some places, it is as deep as 2,600 feet (800 meters), on scale with segments of the Grand Canyon. This immense feature is thought to predate the ice sheet that has covered Greenland for the last few million years.

"One might assume that the landscape of the Earth has been fully explored and mapped," said Jonathan Bamber, professor of physical geography at the University of Bristol in the United Kingdom, and lead author of the study. "Our research shows there's still a lot left to discover."

The scientists used thousands of miles of airborne radar data, collected by NASA and researchers from the United Kingdom and Germany over several decades, to piece together the landscape lying beneath the Greenland ice sheet.

A large portion of this data was collected from 2009 through 2012 by NASA's Operation IceBridge, an airborne science campaign that studies polar ice. One of IceBridge's scientific instruments, the Multichannel Coherent Radar Depth Sounder, operated by the Center for the Remote Sensing of Ice Sheets at the University of Kansas, can see through vast layers of ice to measure its thickness and the shape of bedrock below.

In their analysis of the radar data, the team discovered a continuous bedrock canyon that extends from almost the center of the island and ends beneath the Petermann Glacier fjord in northern Greenland.

At certain frequencies, radio waves can travel through the ice and bounce off the bedrock underneath. The amount of times the radio waves took to bounce back helped researchers determine the depth of the canyon. The longer it took, the deeper the bedrock feature.

"Two things helped lead to this discovery," said Michael Studinger, IceBridge project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It was the enormous amount of data collected by IceBridge and the work of combining it with other datasets into a Greenland-wide compilation of all existing data that makes this feature appear in front of our eyes."

The researchers believe the canyon plays an important role in transporting sub-glacial meltwater from the interior of Greenland to the edge of the ice sheet into the ocean. Evidence suggests that before the presence of the ice sheet, as much as 4 million years ago, water flowed in the canyon from the interior to the coast and was a major river system.

"It is quite remarkable that a channel the size of the Grand Canyon is discovered in the 21st century below the Greenland ice sheet," said Studinger. "It shows how little we still know about the bedrock below large continental ice sheets."

The IceBridge campaign will return to Greenland in March 2014 to continue collecting data on land and sea ice in the Arctic using a suite of instruments that includes ice-penetrating radar.

Paleofluvial Mega-Canyon Beneath the Central Greenland Ice Sheet - Jonathan L. Bamber et al

• Science 341(6149) 997 (30 Aug 2013) DOI 10.1126/science.1239794

Massive ‘Grand Canyon’ Found Hidden Beneath Greenland’s Ice
Universe Today | Nancy Atkinson | 2013 Aug 29

[BDanielMayfield]

Someday when the Earth has moved out of its present glacial period and Greenland is as green as its name implies the river inside this canyon might provide one of the wildest (and coldest) whitewater experiences on the planet.

That’s looking on the bright side of global warming. The dark side is flooding every coastal area on Earth. The Greenland ice sheet contains 2,850,000 cubic kilometers of ice, and were it to melt, (which it will, the only question is how quickly) it would raise global sea level by over 7 meters.

[Beyond]

You sure about the 7 meters? Seems like way-to-much to me.

[BDanielMayfield]

You sure about the 7 meters? Seems like way-to-much to me.

A fair question Beyond, since I failed to supply any supporting proof. Ask and ye shall receive:

The Greenland ice sheet (Greenlandic: Sermersuaq) is a vast body of ice covering 1,710,000 square kilometres (660,235 sq mi), roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. The ice sheet is almost 2,400 kilometres (1,500 mi) long in a north-south direction, and its greatest width is 1,100 kilometres (680 mi) at a latitude of 77°N, near its northern margin. The mean altitude of the ice is 2,135 metres (7,005 ft).[1] The thickness is generally more than 2 km (1.24 mi) and over 3 km (1.86 mi) at its thickest point. It is not the only ice mass of Greenland – isolated glaciers and small ice caps cover between 76,000 and 100,000 square kilometres (29,344 and 38,610 sq mi) around the periphery. Some scientists predict that climate change may be near a "tipping point" where the entire ice sheet will melt in about 2000 years.[2] If the entire 2,850,000 cubic kilometres (683,751 cu mi) of ice were to melt, it would lead to a global sea level rise of 7.2 m (23.6 ft).

[Beyond]

ha-ha, i didn't really ask, but thanks. There seems to be a hell-of-a-lotta ice on Greenland I wonder if they took into account all the extra moisture that would be floating about the atmosphere. Not all the melted water makes it to the ocean.

[BDanielMayfield]

I wonder if they took into account all the extra moisture that would be floating about the atmosphere. Not all the melted water makes it to the ocean.

The lower atmosphere is a very poor sink for holding much more moisture. I read somewhere that if all the water in the atmosphere fell out as rain it would only raise sea level by about 2 inches.

But up in the thermosphere perhaps?

[Beyond]

I just looked on a global map and saw how BIG Greenland is. I would say that it compares to Africa. Africa is BIG

[Chris Peterson]

I just looked on a global map and saw how BIG Greenland is. I would say that it compares to Africa. Africa is BIG :!:

Got to pick those map projections carefully when looking at high latitudes. Greenland is about the same size as Algeria. Africa is 14 times larger than Greenland.

[Chris Peterson]

ha-ha, i didn't really ask, but thanks. There seems to be a hell-of-a-lotta ice on Greenland

You betcha. This is what it looked like just a few hours ago from 42,000 feet. And that's the edge. Look at those peaks at the top just poking through, and imagine the rest of the mountains under the ice.

I wonder if they took into account all the extra moisture that would be floating about the atmosphere. Not all the melted water makes it to the ocean.

For all practical purposes, it does. The amount of water in the atmosphere doesn't change very much over a wide range of climatic conditions, and only represents about 0.001% of the Earth's water supply.

[Beyond]

Ok, so how big is Algeria I'm not about to try and wade through wrong size maps again.

[Chris Peterson]

Ok, so how big is Algeria :?: I'm not about to try and wade through wrong size maps again.

Well, it's obviously a lot smaller than Africa!

[Beyond]

Ah, Algeria is in the upper left of Africa. Well, i just don't see how something that size could have enough ice on it, that if it all melted, it would raise the oceans 7 meters.
Maybe I'm just dense.

[Chris Peterson]

Ah, Algeria is in the upper left of Africa. Well, i just don't see how something that size could have enough ice on it, that if it all melted, it would raise the oceans 7 meters.
Maybe I'm just dense. :lol2:

Just do the math. The approximate volume of the Greenland ice sheet is 1.7 million square kilometers by 2 kilometers thick. Divide by the area of the Earth's ocean, 360 million square kilometers, and you get a rise of 9 meters. Pretty much in line with estimates.

[Beyond]

Hmm... perhaps the 2.2 meter difference is because water expands when it freezes, so in melted form it will be less volume than when frozen

[Chris Peterson]

Hmm... perhaps the 2.2 meter difference is because water expands when it freezes, so in melted form it will be less volume than when frozen :?:

I expect the difference is simply that between an accurately calculated ice volume and my back-of-the-envelope estimate based on area and assumed average thickness.

[geckzilla]

If they weren't completely polluted with our trash, flooded urban areas would make for some interesting habitats for fish. Something like this except with buildings and streets instead of a few benches and trails.

Click to play embedded YouTube video.

[Beyond]

The movie Water World would be an overly extreme example of this flooded meadow

[BMAONE23]

Fortunately, there isn't enough water on, in, or suspended above the Earth to create the fictional "Waterworld" where Dry Land is the top 2000" or so of Mt Everest (really Hawaii).
My dad told me once that if ALL the surface ice were to melt, sea levels wouldn't raise more than 450' though I believe it is more like 250'. Problem is, I live at 62'. So, lets not get too gung ho about transporting Ice Bergs anywhere for fresh water.

[Beyond]

I'm at 500 feet plus, but most of Rhode Island would be ocean bottom. At least i wouldn't have far to go to get to the beach.

[BDanielMayfield]

So I was wondering, how much does 2,850,000 cubic kilometers of ice weigh, and what would be the effects of removing this weight off Greenland and redistributing the weight all across the world ocean? So I Google searched the question “How much does ice weigh?” and found this:

“Like an object that floats on water, analogously the Earth’s crust “floats” in equilibrium on the viscous plastic rocks of the underlying mantle. A decrease in the weight of the crust, caused, for example by the removal of rocks due to erosion, makes the rocks lighter and the crust rises, while an increase in the weight makes the crust sink even deeper into the “soft” and viscous mantle, by a process called isostasy. The formation of thick layers of ice, (as in the glaciations of the past), causes an overload on the ice covered crust, and the result is that it sinks into the mantle, various hundreds of metres, in some cases even below sea level. Knowing the average density of ice and its thickness, it is easy to calculate its weight at the base. At present, due to the weight of the ice-sheet, which reaches 4.5 km in some parts, the Antarctic has sunk over 900 m. Radar measurements carried out in Greenland show that one third of the rock base is below sea level and the weight of the accumulated ice has pushed the rock downwards by over 600 m in some parts. As the large ice-sheets retreat after the last glaciation, the territories that are freed of the weight of the ice have started to rise. For example, the region around the Hudson Bay has risen over 300 m in a little over 10,000 years after the Laurentide ice-sheet retreat. This rise is not over as the territory still has not reached its height before the last glaciation. Also the Scandinavian peninsula is still rising at a rhythm that reaches 9 mm per year in the middle of the Gulf of Bothnia. The delay in the response to the removal of the load is due to the viscosity of the material of the mantle, which has a certain amount of inertia. The rise after the end of the last glaciation is greatly camouflaged by the rise in the sea level as a consequence of the melting of large quantities of continental ice.”

That didn’t exactly answer my how much does ice weigh question, but it did address the second part of my inquiry. Removal of Greenland’s ice in addition to causing sea level rise will cause Greenland to rebound by hundreds of meters. But the added weight of the waters across the Earth’s vast ocean basins will also press down on the ocean seafloor, pushing it down. This will literally raise the continental landmasses over time, partially compensating for the rise of sea level.

[Chris Peterson]

Removal of Greenland’s ice in addition to causing sea level rise will cause Greenland to rebound by hundreds of meters. But the added weight of the waters across the Earth’s vast ocean basins will also press down on the ocean seafloor, pushing it down. This will literally raise the continental landmasses over time, partially compensating for the rise of sea level.

It won't compensate in any meaningful way, given the radically different times scales of sea level change and continental rebound. After all, the rebound presently occurring in North America can't began to keep up with recent sea level rises.

The good news, however, is that continental rebound will eventually allow archaeologists to investigate the several thousand year old remains of New York and Miami without needing to dive.

[Beyond]

The good news, however, is that continental rebound will eventually allow archaeologists to investigate the several thousand year old remains of New York and Miami without needing to dive.

Sometimes "good news" doesn't really seem all that good.

[BMAONE23]

So I was wondering, how much does 2,850,000 cubic kilometers of ice weigh, and what would be the effects of removing this weight off Greenland and redistributing the weight all across the world ocean? So I Google searched the question “How much does ice weigh?” and found this:

“Like an object that floats on water, analogously the Earth’s crust “floats” in equilibrium on the viscous plastic rocks of the underlying mantle. A decrease in the weight of the crust, caused, for example by the removal of rocks due to erosion, makes the rocks lighter and the crust rises, while an increase in the weight makes the crust sink even deeper into the “soft” and viscous mantle, by a process called isostasy. The formation of thick layers of ice, (as in the glaciations of the past), causes an overload on the ice covered crust, and the result is that it sinks into the mantle, various hundreds of metres, in some cases even below sea level. Knowing the average density of ice and its thickness, it is easy to calculate its weight at the base. At present, due to the weight of the ice-sheet, which reaches 4.5 km in some parts, the Antarctic has sunk over 900 m. Radar measurements carried out in Greenland show that one third of the rock base is below sea level and the weight of the accumulated ice has pushed the rock downwards by over 600 m in some parts. As the large ice-sheets retreat after the last glaciation, the territories that are freed of the weight of the ice have started to rise. For example, the region around the Hudson Bay has risen over 300 m in a little over 10,000 years after the Laurentide ice-sheet retreat. This rise is not over as the territory still has not reached its height before the last glaciation. Also the Scandinavian peninsula is still rising at a rhythm that reaches 9 mm per year in the middle of the Gulf of Bothnia. The delay in the response to the removal of the load is due to the viscosity of the material of the mantle, which has a certain amount of inertia. The rise after the end of the last glaciation is greatly camouflaged by the rise in the sea level as a consequence of the melting of large quantities of continental ice.”

That didn’t exactly answer my how much does ice weigh question, but it did address the second part of my inquiry. Removal of Greenland’s ice in addition to causing sea level rise will cause Greenland to rebound by hundreds of meters. But the added weight of the waters across the Earth’s vast ocean basins will also press down on the ocean seafloor, pushing it down. This will literally raise the continental landmasses over time, partially compensating for the rise of sea level.

1 cubic meter of water weighs 1000 kilograms or 2200lbs. There are 1,000,000,000 (billion) cubic meters in a cubic kilometer so a cubic kilometer of water weighs 1,000,000,000,000 (trillion) kilograms or 2,200,000,000,000 pounds

Datsa lotta watta

[geckzilla]

The good news, however, is that continental rebound will eventually allow archaeologists to investigate the several thousand year old remains of New York and Miami without needing to dive.

Sometimes "good news" doesn't really seem all that good.

I should fill a hard drive or perhaps something with better storage retention and put it in a time capsule for them to find before I leave. I could take photos of traffic jams and record audio files of people angrily honking at one another over the split second pause someone made after a light turned green. I could write a journal entry about people getting angry at the post office or grocery store because there is a long line and another about the sleepless nights I encountered when first moving here because of the airplanes and streetlights. A longer, more upbeat section would have to be devoted to the multicultural food selection available nearly within arm's reach. And then I could write about how people of different races all came together in one city and got along for the most part but they still all congregated in their own racially segregated neighborhoods and talk trash about the others behind their backs.

[stephen63]

Ice Station Zebra, and beyond.

http://peopleus.blogspot.com/2011/05/ic ... zebra.html