Helheim Glacier, Greenland - 130-foot Thinning, 4.5-Mile Retreat 2001-05

[hatrack]

EDIT

The researchers used satellite images to determine the movement and retreat of Helheim glacier. Howat tracked the positions of glacial surface features to assess how fast the glacier moved between satellite fly-bys. Satellite images dating back as far as the 1970s show that the front of the glacier has remained in the same place for decades. But in 2001 it began retreating rapidly, moving back four and a half miles between 2001 and 2005. Howat's measurements also show that the Helheim glacier has sped up from around 70 feet per day to nearly 110 feet per day and thinned by more than 130 feet since 2001.

As the glacier speeds up and retreats, new factors come into play that cause further acceleration and retreat, Howat said. "This is a very fast glacier, and it's likely to get faster," he said.

The Helheim glacier is a river of ice that pours from the inland Greenland ice sheet, through a narrow rift in the coastal mountain range, and down into the sea at a rate of several miles per year. In the sea, the glacier's weight keeps it firmly resting on the bottom, as long as the water depth is less than about nine-tenths of the glacier's thickness. Where the water is deep enough to cause the end of the glacier to float, its front becomes brittle and crumbles into icebergs, Tulaczyk explained.

Warming disrupts the delicate balance between glacier thickness and water depth by melting and thinning the glacier. If the glacier thins beyond a critical point, it becomes ungrounded, floats, and rapidly disintegrates. Temperatures in Greenland have increased by more than five degrees Fahrenheit (three degrees Celsius) over the last decade.

"Outlet glaciers may have been thinning for over a decade," Howat said. "But it’s only in the last few years that thinning reached a critical point and began drastically changing the glacier's dynamics."

The retreating front of the glacier causes it to move down the mountain slope more rapidly. This thins the glacier further, which causes upstream parts of the glacier to perceive a steeper slope and begin moving faster, Tulaczyk said.

Many fiords, the channels carved by glaciers flowing into the sea, are deep with a shallow lip in front. Once the glacier floats off this shallow pinning point, it retreats into deeper water, making further disintegration likely, Howat said.

Reduced friction between ice and rock at the glacier bed can also increase glacier speed. Fiords often widen inland, causing the glacier to grate less heavily at the fiord walls and move faster as it retreats. And ice crystals in fast-moving glaciers can realign, further reducing friction, Howat said.

The Helheim glacier's speedup has already propagated 12.5 miles up the glacier. The center of the Greenland ice sheet is only 150 miles inland, and the researchers worry that the effects of the glacier's retreat will continue to move inland, ultimately decreasing the thickness of the whole ice sheet.

"If other glaciers in Greenland are responding like Helheim, it could easily cut in half the time it will take to destroy the Greenland ice sheet," Howat said. "This is a process we thought was only happening in Antarctica, and now we're seeing that it happens really fast in Greenland."

EDIT

MODS - This is a press release, so I excerpted beyond the four-paragraph limit.

http://currents.ucsc.edu/05-06/11-14/glacier.asp

[HereSince1628]

1. I think the phrase is Drip Drip Drip. . . Kerr plopp!

Don't cha just love icebergs? I mean forget about 2 meter rises in sea level. Just think of all those lovely pale blue mountains of ice floating into the North Atlantic shipping lanes.

Beautiful. Just Beautiful!

[phantom power]

2. Interestingly, to date the *interior* ice is thickening.

It sounds as though this glacial speedup will eventually overtake the central thickening, and the net trend will be a loss of ice, and rise in sea level.

[htuttle]

4. I believe that's due to more precipitation due to warmer weather

It doesn't snow as much at -15F as it does at 15F.

[htuttle]

3. It's probably going to start getting really noisy in Greenland soon

Anyone who has spent a Spring in the North can tell you that the more that ice melts, the faster it melts. One day the pond is frozen, the next day the ice is cracking, and the third day most of the ice is gone.

Air pockets and weaker spots in the ice (where there are more impurities, fractures, etc...) will start collapsing inward, unable to bear the weight of the ice above them. This exposes more surface to the warmer air and the sun. As ice chunks fall, they fall into a rising amount of liquid water, which melts it even faster, and so on, until all the ice is gone, and our coastal cities are underwater.

[HereSince1628]

5. There is nothing so awe inspiring as a canon's roar between yer feet

Ice break up is a hell of an exciting time!

And this one has been waiting for thousands of years

[phantom power]

6. I wonder if Greenland might give rise to a "Lake Missoula" scenario?

http://www.spokaneoutdoors.com/scabland.htm
http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/Scablands0.HTM

Imagine an inland ice-lake, growing on the high ice plateau of Greenland. Dammed up until it breaks through one of the glacial outflow channels. In such a scenario, the sea level would not rise over decades, or years, but 24 hours.

Some say that human flood-myths are a distant memory of such an event. Maybe also the inspiration for Atlantis-myths. Imagine a modern city, like New York, built out on what we now consider "continental shelf," but which was once dry land in a world where water was locked up in glaciers spanning the northern hemisphere. If a massive ice-lake broke out, such a city would be submerged 24 hours later, along with most of that world's other cities, population, culture and technology.

I've always imagined that artifacts of such a civilization would survive inland. But any remains underwater would be inaccessible to future archaeologists, until the re-discovery of scuba, submarines, etc.

[Boomer]

7. Not just high water, but....

Would this sudden influx of water and ice crashing into the oceans be sufficient to cause a tsunami? Even a series of tsunamis as successive waves of ice crashed?

As if the high water levels weren't bad enough.

[phantom power]

9. I believe it would be something like what happened in New Orleans.

The waters rose steadily. Not a wave, but still fast enough to trap many people.

[kestrel91316]

8. Hey, life is going to get a WHOLE LOT SIMPLER for the scientists

who study the atmospheric gas content of ice cores. They won't have to study ice cores from Greenland or Antarctica anymore. They can just take a really long vacation. Then they can study the gas content of the ice cubes in our freezers, which is the only place it will be found anymore.