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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 1199849 times)

Iceismylife

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1800 on: February 14, 2017, 01:07:36 AM »
http://go.nasa.gov/2kN1jE4

The fjord is clear of cloud cover some good high res photos would be nice.  See what the winter did.

Oddmonk

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1801 on: February 14, 2017, 05:26:47 PM »
Jakobshavn is calving:

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1802 on: February 15, 2017, 02:10:49 AM »
Not calving. Just sea ice in the Fjord breaking up.

Oddmonk

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1803 on: February 15, 2017, 03:14:15 AM »
I see now, thank you, Shared Humanity. My : should have been ?

Iceismylife

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1804 on: February 16, 2017, 04:19:13 AM »
I'm dying to see some good high res photos of what the calving face looks like.  Anyone care to upload any?

Wipneus

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1805 on: February 16, 2017, 10:37:49 AM »
Extremely big animation (11.5Meg) works on this side.
Using both sentinel 1A and 1B gives an opportunity to have 1 frame per 6 days covering most of the dark season. Everything is scaled to 40m/pixel.
There is surprisingly little calving and the glacier has thus extended considerably. 

Of course you must click to start the animation.

BTW, there are no suitable optical hi-res images yet: Landsat has only cloudy scenes and Sentinel is not reaching this far north yet (but will do so soon).
« Last Edit: February 16, 2017, 10:44:48 AM by Wipneus »

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1806 on: February 16, 2017, 11:02:29 AM »
Thanks Wipneus, it's looking positively fluid with several sidestreams flowing easily. Stunning.

Oddmonk

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1807 on: February 16, 2017, 02:47:28 PM »
Thank you Wipneus! The animations help considerably to better interpret the satellite images. It seems as though the glacier and tributaries in the accumulation zone have been flowing continuously. Does this represent loss, or normal winter movement? I'm eager to understand how it works, if someone has time to elaborate briefly.

Edit: just found the dissertation on glaciers by A-Team and others on the Petermann Gletscher thread.
« Last Edit: February 16, 2017, 03:11:33 PM by Oddmonk »

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1808 on: February 16, 2017, 03:13:52 PM »
Seems fast. Can we get a speed calculated from these images?

Wipneus

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1809 on: February 18, 2017, 12:27:29 PM »
First Landsat.

Click for full size image.
« Last Edit: February 18, 2017, 01:20:54 PM by Wipneus »

Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1810 on: February 19, 2017, 02:31:26 AM »
Seems fast. Can we get a speed calculated from these images?
That's A-teams speciality, but i can give you a rough estimate from the front position.

My time frame is from the last calving on the 12th October to the 9th February (120 days)
In that time the front advanced 105 pixel which is 4200m at 40m resolution. That's 35 meter per day, pretty fast for winter.


iwantatr8

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1811 on: February 19, 2017, 09:42:34 AM »
35m per day seems fast at any time, especially considering the SAR data and updates from the ESA

Go here for more details.

http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=1&image_date=170110_170116#output

I will admit though that they seem to have difficulties in measuring speed close to the calving face.

Oddmonk

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1812 on: February 19, 2017, 01:38:28 PM »
Found this University of Washington news release from 2012:

http://www.washington.edu/news/2014/02/03/greenlands-fastest-glacier-sets-new-speed-record/

They measured Jakobshavn flowing at 46 meters per day during summer. The article calls it Greenland's fastest moving glacier. Wow. Winter hasn't slowed it much? What will it look like this summer?

Adam Ash

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1813 on: February 20, 2017, 08:34:19 AM »
At those velocities the ice at the bedrock interface must be subject to incredible heating due to the forces involved in negotiating the rough floor.  That heat, of course, will be going into the base of the glacier - further reducing the tensile strength of the ice - which will reduce friction and increase the risk of localised bits of the glacier becoming fluidised.  Another nice feedback loop, if you like that sort of thing!

This link gives you an idea of the trivial effort it takes to give temperatures 100s C above ambient.  I suspect a glacier could do better.
http://www.instructables.com/id/Simple-Fire-Piston/

Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1814 on: February 20, 2017, 07:49:46 PM »
A Sentinel 2A image from the 16th February is available. The solar zenith angle is just 81 degrees. (9 degrees above the horizon.) This creates long shadows and reveals steep parts which are normally not visible.

The ice sheet edge is mostly blown snow-free from katabatic winds.

Click on the image for full resolution.

DrTskoul

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1815 on: February 20, 2017, 08:04:31 PM »
Wondrous!!  Belongs to the Arctic image of the day!!

Oddmonk

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1816 on: February 21, 2017, 12:45:06 AM »
Wondrous!!  Belongs to the Arctic image of the day!!

Yes!

Cate

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1817 on: March 10, 2017, 07:53:31 PM »
Eye-balling the Disko area today---in 2016 there was open water all around the island in early March, whereas it still looks pretty ice-bound through the NW channel today. There is a lot more ice sitting in the surrounding waters than last year as well, but it's all rubble-acious. Wind and current play a big role in where the ice sits on any particular day. Toggle years to compare back to 2014.

http://www.arctic.io/explorer/4Xa5A/2017-03-08/8-N69.90254-W52.29753

Anne

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1818 on: March 11, 2017, 11:52:18 AM »
Hotel Arctic's webcam has been showing a frozen bay for some while now but perhaps there's a bit of melt showing this morning.

http://hotelarctic.com/om_hotel_arctic/webcam/

FredBear

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1819 on: March 11, 2017, 01:13:07 PM »
Glacier front looks more advanced this year than the previous 3. Melting season will be interesting.

Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1820 on: March 13, 2017, 10:44:33 PM »
Jakobshavn shows a very interesting calving inactivity. Between the 15th February and 11th March the icebergs just in front of the calving front moved 22-25m per day and the front itself moved 28m per day. Now they are all stuck together and it's very hard to see a distinct front position. If the calving inactivity continues the southern branch will fill the main fjord again and cut the northern branch off. The current front position is about 6.7 km away from the record retreat in 2015.

Click on images for full resolution or to start the gif animation
« Last Edit: March 13, 2017, 11:08:09 PM by Tealight »

Adam Ash

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1821 on: March 16, 2017, 08:44:13 AM »
Does not the lack of a calving face indicate that the terminal section of the glacier has thinned (presumably via bottom melt) to the point where it is now at or close to sea level? 

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1822 on: March 16, 2017, 05:35:50 PM »
Does not the lack of a calving face indicate that the terminal section of the glacier has thinned (presumably via bottom melt) to the point where it is now at or close to sea level?
I highly doubt that bottom melt (really frontal melt as the ice rests on the ground underwater) can eat through hundreds of meters of ice thickness like that, but possibly the front is partially collapsed?

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1823 on: March 17, 2017, 01:49:32 AM »
Spectacular imagery! BTW SNAP-toolbox can be used to track glacier-speed but I think the parameters take some experimenting.

Adam Ash

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1824 on: March 17, 2017, 09:06:04 AM »
Does not the lack of a calving face indicate that the terminal section of the glacier has thinned (presumably via bottom melt) to the point where it is now at or close to sea level?
I highly doubt that bottom melt (really frontal melt as the ice rests on the ground underwater) can eat through hundreds of meters of ice thickness like that, but possibly the front is partially collapsed?

But there is no 'step' to be seen in the glacier anywhere near where the face is/was is there?  There seems to be a continum in the surface gradient from the melange field to points far east.  I guess time, and new imagery, will tell.

Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1825 on: March 21, 2017, 12:23:51 AM »
Spectacular imagery! BTW SNAP-toolbox can be used to track glacier-speed but I think the parameters take some experimenting.
I played a bit around with the offset tracking tool, but couldn't get it to work for S2A images without orbit data. It's not surprising since it is designed for S1A/B with an orbital file and other metadata.

The calving inactivity makes it easier to roughly calculate the ice volume that is pushed out of the ice sheet. The comparison is again against the 2015 record retreat.

area increase: 26.77 km2
thickness: 800m-900m

volume: 21-24 km3
mass: 19.2-21.6 Gt

If the DMI Surface Mass Budget model is correct then in the blue area fit 4% of the annual snowfall over all of Greenland.
http://beta.dmi.dk/en/groenland/maalinger/greenland-ice-sheet-surface-mass-budget/

VeliAlbertKallio

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"Setting off atomic bombs is considered socially pungent as the years are made of fleeting ice that are painted by the piling up of the rays of the sun."

crandles

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1827 on: April 07, 2017, 12:54:59 AM »
The satellite image shows little sea ice and ice bergs in the Ilulissat Ice Fjord. Where the bergs and sea ice gone? Should there be some form of ice in the Ice Fjord?

Flushing events do happen from time to time. Seems quite a large chunk starting moving out on 4th April and has since broken up. Currents can set up so warm salty water moves in beneath the surface, melts the glacier diluting salt content and gets cooled but is less dense due to salt content moves up to surface/just below melange and flows out of the fjord. Sometimes there is too much ice (plus large iceburgs grounded) and it jams up and other times it doesn't jam and flows out with outward near surface current. (I think.)

Cate

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1828 on: April 07, 2017, 01:51:53 PM »
crandles, thank you for the explanation about flushing. I too had been wondering about that sudden outflow.

Btw, that general Disko area seems to have a lot more ice around in all the channels and bays than last year at this time, when it was all open water up there along the Greenland side of Baffin Bay.
« Last Edit: April 07, 2017, 02:00:32 PM by Cate »

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1829 on: April 07, 2017, 02:10:28 PM »
The satellite image shows little sea ice and ice bergs in the Ilulissat Ice Fjord. Where the bergs and sea ice gone? Should there be some form of ice in the Ice Fjord?
If you zoom [ctrl+] in on this you'll see there's been fresh water showing up south of Disko for some time, probably from melt in the fjord. https://www7320.nrlssc.navy.mil/hycomARC/navo/arcticsss_nowcast_anim30d.gif
It's been like that since early feb. though a little more ambiguous, the current flowing into the fjord is relatively warm and very saline so probably melting the base of the big bergs.

VeliAlbertKallio

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1830 on: April 07, 2017, 02:50:55 PM »
Hi John, if that is so, I find it somewhat surprising that on the link you provide there is even bigger source of ice bergs (?) and freshwater on the South-Easternmost corner section of Greenland. What is loading the ocean there with freshwater, as I have understood Ilulissat being the most active loader of ice and freshwater(?) What do you think is the source of there of that steep blue colour in your link?

The satellite image shows little sea ice and ice bergs in the Ilulissat Ice Fjord. Where the bergs and sea ice gone? Should there be some form of ice in the Ice Fjord?
If you zoom [ctrl+] in on this you'll see there's been fresh water showing up south of Disko for some time, probably from melt in the fjord. https://www7320.nrlssc.navy.mil/hycomARC/navo/arcticsss_nowcast_anim30d.gif
It's been like that since early feb. though a little more ambiguous, the current flowing into the fjord is relatively warm and very saline so probably melting the base of the big bergs.
"Setting off atomic bombs is considered socially pungent as the years are made of fleeting ice that are painted by the piling up of the rays of the sun."

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1831 on: April 07, 2017, 08:58:32 PM »
"What do you think is the source of there of that steep blue colour in your link?"
There's warm basal waters escaping from the Arctic, plus recycled Atlantic waters flowing down the east coast, they can both be drawn into the fjords by tidal flows, some of the fjords run deep, http://membrane.com/sidd/greenland-2013/45-090.jpg , the warmer the water and the larger the tidal range the more meltwater flows out. If you run the 12 month sss animation you'll see plenty of 'blue' even as far north as 79N/Zacharaie. https://www7320.nrlssc.navy.mil/hycomARC/arctic.html

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1832 on: April 11, 2017, 10:00:33 PM »
New bed elevation data for Jacobshawn from doi:10.1002/2017GL073245

I attach a section of Fig 1a)


pileus

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1833 on: April 11, 2017, 10:14:03 PM »
Found this to be a very concise and easy to understand article for the non-technically inclined.  The WAPO has done a nice job in the last year or two with an increasing level of focus on the actual science, and avoiding the insertion of denialist POV in every article.

https://www.washingtonpost.com/news/energy-environment/wp/2017/04/11/scientists-just-uncovered-some-troubling-news-about-greenlands-most-enormous-glacier/?utm_term=.71d016825c0d

--------------

But until now, researchers have not been sure how far Jakobshavn’s ice extends below sea level — or how much deeper it gets further inland. That’s crucial because Jakobshavn is undergoing a dangerous “marine ice sheet instability,” in which oceanfront glaciers that grow deeper further inland are prone to unstoppable retreat down what scientists call a “retrograde” slope.

That’s where the new science comes in: Researchers who flew over Jakobshavn in a helicopter toting a gravimeter, used to detect the gravitational pull of the ice and deduce its mass, say they’ve found the glacier extends even deeper below sea level than previously realized, a configuration that sets the stage for further retreat.

“The way the bed looks, sort of makes it more prone to continuous retreat for decades to come,” said Eric Rignot, a researcher with NASA’s Jet Propulsion Laboratory and the University of California-Irvine, one of the authors of the new study.

bairgon

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Adam Ash

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1835 on: April 15, 2017, 05:49:33 AM »
Great views of the Jakobshavn canyon in the video on this page
https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4097

Video at:  'The Earth layer alone with transparency at gamma 1.0.'

The Jk canyon is big enough, but the canyon feeding Petermann gives a direct connect to all of inland Greenland.  Huge, and its already melting into a groove...
http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/?utm_term=.62144c2fdb37

Lennart van der Linde

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1836 on: April 15, 2017, 07:59:00 AM »
Sidd referred to An et al 2017, Bed elevation of Jakobshavn Isbrae, West Greenland,
from high-resolution airborne gravity and other data:
http://sci-hub.cc/10.1002/2017GL073245

Abstract
Jakobshavn Isbrae, West Greenland, which holds a 0.6-m sea level volume equivalent, has been speeding up and retreating since the late 1990s. Interpretation of its retreat has been hindered by diculties in measuring its ice thickness with airborne radar depth sounders. Here, we employ high-resolution, helicopter-borne gravity data from 2012 to reconstruct its bed elevation within 50 km of the ocean margin using a three-dimensional inversion constrained by fjord bathymetry data offshore and a mass conservation algorithm inland. We fi nd the glacier trough to be asymmetric and several 100 m deeper than estimated previously in the lower part. From 1996-2016, the grounding line migrated at 0.6 km/yr from 700 m to 1,100 m depth. Upstream, the bed drops to 1,600 m over 10 km then slowly climbs to 1,200 m depth in 40 km. Jakobshavn Isbrae will continue to retreat along a retrograde slope for decades to come.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1837 on: April 18, 2017, 08:18:31 PM »
Thanks for that sidd and Lennart.
 There's ongoing melt water flowing into Baffin, less ambiguous than earlier in the year, and the ice jam's broken from it's winter position. If it all flows past the outer cill we may see some movement further in soon.


Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1838 on: April 22, 2017, 12:18:07 AM »
Jakobshavn Isbrae calved again!

Judging from NASA Worldview it was probably on the 19th April, but we only have high resolution Sentinel 2A images from the 15th and 20th. On the 15th the front position was close to the one in 2004/2005 and almost extended beyond the division between north and south branch. After the calving, the front moved 1.8 km inland to the 2006 level.



The first images is from the 15th April and the second from the 20th April. Click for full resolution.




sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1839 on: April 22, 2017, 12:52:13 AM »
" ...  front position was close to the one in 2004/2005 ... "

 The calving front is not the same as the groundling line, is it ?

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1840 on: April 22, 2017, 01:00:35 AM »
As I understand it, JH lost its ice shelf some years back and is now grounded at the calving front.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1841 on: April 22, 2017, 01:39:12 AM »
Looking at some of the calved bergs, they haven't tuned over so were floating [?], not grounded, with the tides building an interesting week ahead.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1842 on: April 22, 2017, 05:42:13 PM »

The glacier can extend down to bedrock and calve, the smaller chunks of ice then float.

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1843 on: April 22, 2017, 06:37:14 PM »
Looking at some of the calved bergs, they haven't tuned over so were floating [?], not grounded, with the tides building an interesting week ahead.

Some have tipped. Some have not. Some, based on their size, seem to have fractured and then tipped. Not sure you can draw conclusions about grounding line from this.

Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1844 on: April 22, 2017, 10:13:10 PM »
The bedrock in the fjord is quite irregular varying between 400-600m below sea level and the deepest parts are under 1200m below sea level. Additionally the bedrock is only known to a 100-200m resolution so no one can tell you exactly where the grounding line is. It is probably not a real line and more a few sections where the ice floats and a few where the ice is grounded.

The thickest icebergs I have measured are close to 900m thick and likely drag along the bedrock. 

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1845 on: April 23, 2017, 02:04:19 AM »
I'm thinking there may be no definitive grounding line hereabouts, sure it's grounded either side to some extent, but in the main channel there may be contact in places, and possibly not. I suspect the large peices that didn't overturn may be the deepest/thickest, it's a pity the new bed elevation doesn't extend further west, which could give us a clue to the thickness of the ice stream when/if these peices get stuck. Curiously looking at the behaviour of the ice stream my guess was that the deep saline water was likely continuous below 750m and probably not so much above 600m where there's enough ice to displace it, that would work with ice 900m thick. So if they pass the inner cills, unless it's very warm they won't pass the outer cill for a whle, we'll see.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1846 on: April 28, 2017, 11:15:14 PM »
It looks like the floating ice is flushing from the fjord.

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1847 on: April 29, 2017, 05:03:47 PM »
The fjord is always pretty full of icebergs and they also flush out.

Ajpope85

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1848 on: May 03, 2017, 03:42:08 PM »
Worldview caught a pretty calving event.

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1849 on: May 03, 2017, 06:00:23 PM »
Worldview caught a pretty calving event.


Ajpope85, no what you are watching is sea ice in the fjord breaking up.
Have a ice day!