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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 721853 times)

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2000 on: January 11, 2019, 03:02:19 PM »
Glacier-ice is malleable at depths of 30m and deeper. Therefore the ice-stream channel must be full of ice until the grounding-line (which for Jakobshavn is estimated to reside within ~1km of the calving front depending on the season) even if the depth of the channel varies. That being said, meltwater channels do form under the ice-stream.

Quote
Surface meltwater-induced velocity variation is a quasi-diurnal signal. Podrasky et al. (2012) detected an amplitude of up to 0.1 m d−1 diurnal signal 20–50 km upstream from the terminus of Jakobshavn Isbræ

https://search.proquest.com/openview/2b991b9bb1ea4dbf97777598550b275e/1?pq-origsite=gscholar&cbl=105732

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2001 on: January 12, 2019, 02:04:41 AM »
Glacier-ice is malleable at depths of 30m and deeper. Therefore the ice-stream channel must be full of ice until the grounding-line (which for Jakobshavn is estimated to reside within ~1km of the calving front depending on the season) even if the depth of the channel varies. That being said, meltwater channels do form under the ice-stream.

Quote
Surface meltwater-induced velocity variation is a quasi-diurnal signal. Podrasky et al. (2012) detected an amplitude of up to 0.1 m d−1 diurnal signal 20–50 km upstream from the terminus of Jakobshavn Isbræ

https://search.proquest.com/openview/2b991b9bb1ea4dbf97777598550b275e/1?pq-origsite=gscholar&cbl=105732

From what I read it doesnt explain why we have tabular icebergs showing up again?
Have a ice day!

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2002 on: January 13, 2019, 12:28:13 AM »
The grounding line in that paper is what I think of as the strand line, where the wall of ice moving down the fjord actually touches down on bedrock, beyond there upstream I'm thinking it's supported by bouyant dense ice, a melange if you will that fills the chasm. The tabular bergs slide/grind on that melange and are floated west by tidal movement.

johnm33

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johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2004 on: January 15, 2019, 10:53:50 PM »
Some calving taking place, looking at 12:00 the north stream has pushed into the bay, and to the right there's some outflow from area north of what will become the island, the main glacier releases some more tabular bergs some of which have turned.

from Polarveiw
 Grounding line/Strand line, if the glacier is grounded then some real retreat is possible, if it's current calving front is a strand line then the fluidity of the base upstream will inhibit retreat and advance will only be possible if the bergs at the face are small enough to float pass the shallow strand line. I don't think that's likely soon but when it happens it could be quite spectacular, probably needs a clear fjord for the best show. I guess.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2005 on: January 28, 2019, 10:58:47 AM »
Some recent calving, detail from polarview
There's also a feature midstream at the bottom of the image which is what I imagine a giant berg would look like moving in the stream.


Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2006 on: January 28, 2019, 08:02:22 PM »
The tabs are now gone, back to normal calving activity:

Have a ice day!

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2007 on: January 29, 2019, 02:01:24 PM »
There's also a feature midstream at the bottom of the image which is what I imagine a giant berg would look like moving in the stream.
The channel is full of ice upstream from from the grounding-line, so certainly in that position. Thick ice acts like a viscous fluid (like honey).

iwantatr8

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2008 on: February 08, 2019, 01:40:53 PM »
There's an interesting article from cryosphere looking at using machine learning to track calving faces through SAR products - which has the potential to support the overall tracking of major calvings in greenland and antarctica.

https://www.the-cryosphere-discuss.net/tc-2019-14/tc-2019-14.pdf

Stephan

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2009 on: February 08, 2019, 07:51:48 PM »
Thanks for sharing.
And a 'like' earned

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2010 on: February 14, 2019, 04:21:20 PM »
No calving to speak of but about 1km advance polarview



Stephan

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2011 on: February 14, 2019, 07:40:42 PM »
If you look at that Polarview image you can see a lot of frozen summer melt lakes on the ice sheet further inland. They haven't drowned through the moulins.

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2012 on: February 26, 2019, 10:08:27 PM »
Another big calving:
Have a ice day!


b_lumenkraft

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2014 on: Today at 05:00:21 PM »
Greenland's Jakobshavn Glacier Reacts to Changing Ocean Temperatures


vox_mundi

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2015 on: Today at 09:43:44 PM »
Related

Cold Water Currently Slowing Fastest Greenland Glacier
https://www.jpl.nasa.gov/news/news.php?feature=7356

A major Greenland glacier that was one of the fastest shrinking ice and snow masses on Earth is growing again, a new NASA study finds.

The Jakobshavn glacier around 2012 was retreating about 1.8 miles (3 kilometers) and thinning nearly 130 feet (almost 40 meters) annually. But it started growing again at about the same rate in the past two years, according to a study in Monday's Nature Geoscience . Study authors and outside scientists think this is temporary.

A natural cyclical cooling of North Atlantic waters likely caused the glacier to reverse course, said study lead author Ala Khazendar, a NASA glaciologist on the Oceans Melting Greenland (OMG) project. Khazendar and colleagues say this coincides with a flip of the North Atlantic Oscillation—a natural and temporary cooling and warming of parts of the ocean that is like a distant cousin to El Nino in the Pacific.

The water in Disko Bay, where Jakobshavn hits the ocean, is about 3.6 degrees cooler (2 degrees Celsius) than a few years ago, study authors said.

While this is "good news" on a temporary basis, this is bad news on the long term because it tells scientists that ocean temperature is a bigger player in glacier retreats and advances than previously thought, said NASA climate scientist Josh Willis, a study co-author. Over the decades the water has been and will be warming from man-made climate change, he said, noting that about 90 percent of the heat trapped by greenhouse gases goes into the oceans.

"In the long run we'll probably have to raise our predictions of sea level rise again," Willis said.

Interruption of two decades of Jakobshavn Isbrae acceleration and thinning as regional ocean cools, Nature Geoscience (2019)
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