Dear Readers,
This is a must-see animation of the past few days activity of the Jakobshavn
Isbræ. Hats off to Neven at typepad.
Animation 7: Jakobshavn Isbræ by Neven, July 12, 2010
I was planning on having a look at Jakobshavn Glacier some time later this season, but some recent developments made me decide to make an animation now. First off, some basic information from Wikipedia on one of the most important Greenland glaciers:
Jakobshavn Isbræ drains 6.5% of the Greenland ice sheet and produces around 10% of all Greenland icebergs. Some 35 billion tonnes of icebergs calve off and pass out of the fjord every year. Icebergs breaking from the glacier are often so large (up to a kilometer in height) that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord.
Pictures say more than words. The MODIS image of Greenland on the right has a red circle in it showing
where the glacier is located. The pictures on the left are aerial photos from glaciologist David Holland's webpage showing the icebergs calving from the ice front of the glacier, entering the waters of the Disko Bugt, and further up the glacier a picture of the terminus, located about 40 km up-fjord of the mouth.
Some more details from the Recession of Jakobshavn Isbræ article on Mauri Pelto's Glacier Change blog, which I recommend reading in its entirety:
Jakobshavn Isbræ drains 6.5% of the Greenland ice sheet and produces around 10% of all Greenland icebergs. Some 35 billion tonnes of icebergs calve off and pass out of the fjord every year. Icebergs breaking from the glacier are often so large (up to a kilometer in height) that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord.
Pictures say more than words. The MODIS image of Greenland on the right has a red circle in it showing
where the glacier is located. The pictures on the left are aerial photos from glaciologist David Holland's webpage showing the icebergs calving from the ice front of the glacier, entering the waters of the Disko Bugt, and further up the glacier a picture of the terminus, located about 40 km up-fjord of the mouth.
Some more details from the Recession of Jakobshavn Isbræ article on Mauri Pelto's Glacier Change blog, which I recommend reading in its entirety:
The Jakobshavn Isbrae (glacier) has captured our attention over the last 30 years because it has the highest long term average velocity of any glacier in the world. At the ice front the velocity has remained above 16 meters per day for all measurements completed over the last 50 years. The ability of this glacier which is 10 km wide at its front and 800 m thick at the calving front to drain 6.5 % of the Greenland Ice Sheet is its importance.
(...)
From 1964 to 2001 the glacier terminus did not recede significantly and observations of terminus velocity remained relatively constant at 16 to 20 m year at the glacier front. Then in 1997 an acceleration began. The velocity reached 34 m per day by 2003, twice its normal speed, the glacier thinned by up to 15 m year and retreated 10 km, from 2001 to 2003. From 2004-2007 an additional retreat of 5 km occurred.
This picture is showing the retreat of the glacier terminus very nicely (click for a larger version):
So what is the current situation? NASA has the answer:
NASA-funded researchers monitoring Greenland's Jakobshavn Isbrae glacier report that a 7 square kilometer (2.7 square mile) section of the glacier broke up on July 6 and 7, 2010, as shown in the image above [below, red]. The calving front – where the ice sheet meets the ocean – retreated nearly 1.5 kilometers (a mile) in one day and is now further inland than at any time previously observed. The chunk of lost ice is roughly one-eighth the size of Manhattan Island, New York.
(...)
As the glacier has retreated, it has broken into a northern and southern branch. The breakup this week occurred in the north branch.
Scientists estimate that as much as 10% of all ice lost from Greenland is coming through Jakobshavn, which is also believed to be the single largest contributor to sea level rise in the northern hemisphere. Scientists are more concerned about losses from the south branch of the Jakobshavn, as the topography is flatter and lower than in the northern branch.
Here's a close-up of the break-off (images courtesy of DigitalGlobe):
This image is an update from the previous one and has been annotated by Mauri Pelto (the A and the C). As Mauri comments below:
What is fascinating is the speed at which the glacier surface below A at C was transformed from an ordinary set of transverse crevasses to the chaotic scene typically indicative of an area of rapid acceleration and failure of seracs, those walls between crevasses. The glacier has had a profound response to the rift. The area of crevasse transformation is an indication of the connection of this area of the glacier to action at the terminus. The area around C is a zone of weakness to watch for further appearance of rifting. The area in front of the bedrock high is clearly not a place for the terminus to stabilize. The bedrock high itself could well be.
And now finally, the moment everyone has been waiting for, the purpose of this whole article: my animation of the last 7 days. I let them precede by day 172 and 178 to show what the glacier looked like a few weeks ago.
The part in the middle of the fjord with some water showing, looks interesting. I was wondering if the fjord could clear entirely of ice if conditions were right, and even asked Mauri Pelto's opinion on that in a comment on his latest article, but to repeat part of the Wikipedia quote at the start of the article:
Icebergs breaking from the glacier are often so large (up to a kilometer in height) that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord.
So I don't think we'll be seeing that happening some time soon (unfortunately, as it would look really cool).
I have also added two red circles on day 187 (July 6th) because unfortunately this is the best resolution we citizen 'scientists' can get from MODIS, and I had to look really hard to see where the change had taken place. The lower red circle is the area of the northern branch of the terminus where the rift and subsequent retreat takes place. The other red circle provides a orientation point that shows how the whole thing comes sliding down.
Okay, have a good look:
Just before publishing I decided to have a look at the latest MODIS image of this area (day 192) and was surprised to see some sort of local cloud hanging over the glacier and blocking the view. It looks a bit weird, perhaps caused by all the energy that is released when huge chunks of ice break off. So I've decided to add it to the animation. I'd love to hear how you folks interpret this weird cloud and what might be happening under it.
Here's a YouTube movie showing how such a sliding event or retreat looks like from up close (0.35 onwards):
(...)
From 1964 to 2001 the glacier terminus did not recede significantly and observations of terminus velocity remained relatively constant at 16 to 20 m year at the glacier front. Then in 1997 an acceleration began. The velocity reached 34 m per day by 2003, twice its normal speed, the glacier thinned by up to 15 m year and retreated 10 km, from 2001 to 2003. From 2004-2007 an additional retreat of 5 km occurred.
This picture is showing the retreat of the glacier terminus very nicely (click for a larger version):
So what is the current situation? NASA has the answer:
NASA-funded researchers monitoring Greenland's Jakobshavn Isbrae glacier report that a 7 square kilometer (2.7 square mile) section of the glacier broke up on July 6 and 7, 2010, as shown in the image above [below, red]. The calving front – where the ice sheet meets the ocean – retreated nearly 1.5 kilometers (a mile) in one day and is now further inland than at any time previously observed. The chunk of lost ice is roughly one-eighth the size of Manhattan Island, New York.
(...)
As the glacier has retreated, it has broken into a northern and southern branch. The breakup this week occurred in the north branch.
Scientists estimate that as much as 10% of all ice lost from Greenland is coming through Jakobshavn, which is also believed to be the single largest contributor to sea level rise in the northern hemisphere. Scientists are more concerned about losses from the south branch of the Jakobshavn, as the topography is flatter and lower than in the northern branch.
Here's a close-up of the break-off (images courtesy of DigitalGlobe):
This image is an update from the previous one and has been annotated by Mauri Pelto (the A and the C). As Mauri comments below:
What is fascinating is the speed at which the glacier surface below A at C was transformed from an ordinary set of transverse crevasses to the chaotic scene typically indicative of an area of rapid acceleration and failure of seracs, those walls between crevasses. The glacier has had a profound response to the rift. The area of crevasse transformation is an indication of the connection of this area of the glacier to action at the terminus. The area around C is a zone of weakness to watch for further appearance of rifting. The area in front of the bedrock high is clearly not a place for the terminus to stabilize. The bedrock high itself could well be.
And now finally, the moment everyone has been waiting for, the purpose of this whole article: my animation of the last 7 days. I let them precede by day 172 and 178 to show what the glacier looked like a few weeks ago.
The part in the middle of the fjord with some water showing, looks interesting. I was wondering if the fjord could clear entirely of ice if conditions were right, and even asked Mauri Pelto's opinion on that in a comment on his latest article, but to repeat part of the Wikipedia quote at the start of the article:
Icebergs breaking from the glacier are often so large (up to a kilometer in height) that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord.
So I don't think we'll be seeing that happening some time soon (unfortunately, as it would look really cool).
I have also added two red circles on day 187 (July 6th) because unfortunately this is the best resolution we citizen 'scientists' can get from MODIS, and I had to look really hard to see where the change had taken place. The lower red circle is the area of the northern branch of the terminus where the rift and subsequent retreat takes place. The other red circle provides a orientation point that shows how the whole thing comes sliding down.
Okay, have a good look:
Just before publishing I decided to have a look at the latest MODIS image of this area (day 192) and was surprised to see some sort of local cloud hanging over the glacier and blocking the view. It looks a bit weird, perhaps caused by all the energy that is released when huge chunks of ice break off. So I've decided to add it to the animation. I'd love to hear how you folks interpret this weird cloud and what might be happening under it.
Here's a YouTube movie showing how such a sliding event or retreat looks like from up close (0.35 onwards):
Link: http://neven1.typepad.com/blog/2010/07/animation-7-jakobshavn-isbr%C3%A6.html#more
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