Massive Greenland Glacier Retreats One Mile in One Night
Giant Greenland Glacier Cracks Open Overnight
The Arctic's biggest iceberg factory just hit overdrive
Discovery.com, July 13, 2010
It used to be that when a glacier had a bad night it was like that proverbial tree falling in the forest.
Now ice
researchers using several satellites to monitor Greenland's most active
glaciers almost daily have caught the north limb of the
mother-of-all-Greenland glaciers, Jakonbshavn, retreating a mile in a
night.
"A few nights ago
a crack opened up," said Tom Wagner, cryospheric program scientist at
NASA. "Two nights later (July 6) the whole (gosh darned) thing breaks
off and flows away." The lost portion has been described as about an
eighth the size of Manhattan Island and set a new record for the retreat
of that glacier.
But that's not
all. On July 12 there was a new large crack discovered in the glacier's
southern limb as well. Whether that means another gigantic release of
ice or not remains to be seen.
Jakonbshavn is
already well known for being a major exit route for 10 percent of the
ice that leaves Greenland for the sea. The river of ice fills a vast
valley which, if emptied, would rival the Grand Canyon in scale.
It appears that
the record retreat of Jakonbshavn may have been helped by an
exceptionally warm winter, which prevented sea ice from forming in front
of the glacier, said Ian Joughin of the Polar Science Center Applied
Physics Lab at the University of Washington.
There's usually
about four miles of sea ice floating in front of the glacier, keeping
the water nice and chilly near the calving front of the glacier -- and
less prone to calving off icebergs.
Normally the
glacier retreats in the summer, then regains ground in winter as it
surges towards the sea with the help of sea ice. The lack of sea ice
appears to have changed that, say researchers.
"This year it
started (calving) where it left off last summer," said Ian Howat of the
Byrd Polar Research Center at Ohio State University.
In the past,
satellite images could be months or years apart. Over such periods
glaciers can advance and retreat many times, making the few snapshots
only useful for determining long-term trends. For a more detailed study
of just how glaciers behave, a better time-resolution was needed.
"It's exciting
because there's a lot we don't understand," said Joughin. Getting higher
time-resolution images like those that caught Jakonbshavn retreating so
quickly finally lets researchers begin to study the basic principles of
glacier behavior.
The satellites
the researchers are using to keep almost daily tabs on the giant
Jakonbshavn, Kangerlugssuaq, and Helheim glaciers, and weekly checks on
smaller outlet glaciers include DigitalGlobe's WorldView 2, which takes
optical (visible light) images.
When clouds get
in the way, radar images can be used from a German satellite that can
penetrate the cloud cover. Data is also being used from Landsat, Terra,
and Aqua satellites.
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