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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 634121 times)

Wipneus

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1900 on: April 07, 2018, 01:28:09 PM »
Jacobshavn during the dark season in 16 Sentinel 1B images.

crandles

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1901 on: April 07, 2018, 02:27:39 PM »
Wow lots of advance of south branch. When was last time calving front was so far west?

Faster flow prior to rapid retreat?

looked back for one of these


crandles

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1902 on: April 07, 2018, 02:34:47 PM »


back at 2005 position?

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1903 on: April 07, 2018, 03:37:59 PM »
It will probably calve soon. But indeed the calving front of JH has seems to have stopped retreating in the last couple of years. I wonder if this is because of an improvement/slowdown in Greenland melt (as I suspect), or maybe a speedup of the ice flow causing the calving front to extend outwards.
What I always find impressive about JH, beyond its speed, is the constant inflow from its surroundings into the fjord, very visible in the above animation.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1904 on: April 07, 2018, 04:26:50 PM »
Thanks Wipneus, wonderful. Looks like the west side of the north front and the north side of the south front are primed for rapid change if/when the fjord clears, the latter perhaps as soon as the south front retreats. The general increase in flow has to expand the exposed surfaces by orders of magnitude[?] so sunshine or moist air could cause a huge melt.

georged

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1905 on: April 07, 2018, 11:53:46 PM »
Jacobshavn during the dark season in 16 Sentinel 1B images.

Is it possible to estimate the flow rate from those images?


Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1907 on: April 12, 2018, 05:57:32 AM »
Can anyone get a high-res shot of the calving fronts of Jakobshavn for April 10?  Appears to be something going on there, looking at EOSDIS (looks too big to be a cloud's shadow):

Did you mean the 9th April like your link? The dark blob is the shadow of a low cloud. A later date is not yet available.

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1908 on: April 14, 2018, 03:54:06 PM »
Jacobshavn during the dark season in 16 Sentinel 1B images.

Is it possible to estimate the flow rate from those images?
Yes, for example with the ESA SNAP toolbox.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1909 on: April 14, 2018, 11:29:56 PM »
Full resolution from polar veiw 46mb. I think these are archived for a while unlike the zoomables

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1910 on: May 01, 2018, 10:35:38 PM »
I was looking at Hycom earlier it looked like there was an outflow of fresh-water from Disko, presumably Jakobshavn. Luckily there's a zoomable today courtesy of polarview. The ice dam appears to have broken out, there are even waves apparent flowing from the fjord. The previous link ^ still works for now.
« Last Edit: May 01, 2018, 11:38:45 PM by johnm33 »

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1911 on: May 01, 2018, 10:58:09 PM »
Burton et al have a paper out in PNAS on the melange in front of Jacobshawn. It is a brave effort, and they actually did lab simulations with plastic icebergs. And numerical models. And incorporated field data.

Their results are passable but not very remarkable, but I attach fig 1 whose panel B is a velocity map of the melange.

doi: 10.1073/pnas.1715136115

sidd

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1912 on: May 02, 2018, 10:59:37 PM »
Unexpected and for some reason not reported anywhere, Jakobshavn Isbræ is "advancing" and we may soon see the Northern Branch joining the Southern Branch, I doubt it is a real advance though, could it be a mix of thinning and "softer" ice?
But still it is a pretty unusual behavior of a West Coast Glacier, where almost all Glaciers are status quo or retreating. 

The image below the animation is taken on April 30 2018 by Nasa Ice Bridge 2018, showing the Split Island between the Northern and Southern Branch.
Have a ice day!

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1913 on: May 03, 2018, 12:03:41 AM »
Very strange indeed.  I keep expecting for it to calve, but this is way beyond typical variation.

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1914 on: May 03, 2018, 12:57:32 AM »
Very strange indeed.  I keep expecting for it to calve, but this is way beyond typical variation.

It would seem to have to be related to the characteristics of the ice itself. What type of glacier ice would be less prone to calving? How does the calving front differ from previous years which showed a fairly persistent behavior of advance and calving.

Adam Ash

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1915 on: May 03, 2018, 03:48:11 AM »
Could it be that colder ice is more prone to brittle failure and warmer ice is more inclined to move via plastic flow?  Thence, the reduction in calving events (brittle failures) and the recently-observed 'extrusion' of the ice streams could be indicative of higher ice temperatures in depth.  That in turn would imply less energy needed to complete its melt.  ??

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1916 on: May 03, 2018, 05:13:56 AM »
That Burton paper found that there was considerable back stress transmitted from fjord walls to the calving front by the melange, which would act to suppress calving.

sidd

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1917 on: May 03, 2018, 09:51:29 AM »
I've been thinking that the northern[western] branch has felt the power of the sun more than the rest and has a more fluid base. I expect it to rapidly retreat to it's former calving front once the melange has broken and cleared, unless it has itself cleared a cill in that area, in which case I suppose it will simply continue to flow more rapidly.
 At some point the largest consolidated icebergs formed in the deepest parts of the fjord, upstream will all have passed through to Disko, then it's a possibility that the more broken ice falling into the fjord will not be sufficiently large to ground themselves in passage, and the melange will not provide so much resistance.
It's worth taking a look at Iwantatr8' animation from last year, https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=154.0;attach=44891;image might need a click.

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1918 on: May 16, 2018, 07:16:16 PM »
Continuing expansion at both the southern branch and northern branch. The southern calving front will soon pass Split Ø.
Have a ice day!

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1919 on: May 17, 2018, 04:37:25 PM »
Amazing. Could there be a qualitative difference in the physical characteristics of the glacier ice which could be contributing to this rapid growth in the glacier?

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1920 on: May 18, 2018, 04:32:15 PM »
The fjord is full, the western face of the northern branch has calved and the main glacier too.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1921 on: May 23, 2018, 10:43:28 AM »
Just checked to see if the fjord has jammed up, it looks free to flow, so we should see some action during the next full moon tidal cycle.


top image from polarview

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1922 on: May 23, 2018, 09:51:20 PM »
As noted by Johnm above, a new development is underway, tabular icebergs not seen in many years are now present at the Southern Branch of Jakobshavn Isbræ: 
Have a ice day!

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1923 on: May 23, 2018, 09:56:58 PM »
I wonder if one could calculate the reduction in backstress a la the Burton paper from th size and distribution of tabular icebergs released after melange is flushed away ?

sidd

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1924 on: May 23, 2018, 10:32:27 PM »
I wonder if the tabular icebergs plus "no calving policy" might signify a reduction in height of the JH front? This is probably easily disproved by satellite altimetry, but where to find current data?

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1925 on: May 23, 2018, 10:36:34 PM »
Radar altimetry cannot resolve something as narrow, deep and complex and Jakobshaven calving front. Measuring shadow-length from VHR optical/SAR imagery does work but the data is scarce.

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1926 on: May 23, 2018, 10:39:06 PM »
As noted by Johnm above, a new development is underway, tabular icebergs not seen in many years are now present at the Southern Branch of Jakobshavn Isbræ:

For this change to have occurred at the same time we are seeing dramatic growth in the glacier cannot be a coincidence. Something significant is happening.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1927 on: May 23, 2018, 11:26:19 PM »
I revisited polarview to take another look and found a new image only 12hrs. after the first, I'd earlier thought there was a separate stream flowing from the northern branch, so

Here's a link to sentinel that shows the streams in better detail.

FredBear

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1928 on: May 24, 2018, 06:38:49 PM »
Surely IceBridge should have produced data on the heights of the glacier front over the past few years?
I also wonder what is producing the surface flow which is flushing the icebergs out of the fiord - probably a combination of:-
(1) Warm deep saline water melting the base of the glacier
(2) Geothermal melt from the upstream glacier
(3) Summer surface melt (but it starts too early!)
???
« Last Edit: May 26, 2018, 10:40:01 AM by FredBear »

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1929 on: May 24, 2018, 10:03:05 PM »
If these tabular icebergs survives the voyage down the fjord, there will be something to watch from the shores around Ilulissat and probably make some front page stories in the media.
Have a ice day!

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1930 on: May 26, 2018, 11:28:29 AM »
A detail from the 25th showing the separate northern stream

One of the clearest days so far this year well worth a look around if your inclined. I set the effects to gain .3 gamma 1.9  with atmospheric correction ymmv.

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1931 on: Today at 08:26:29 AM »
Can anyone get a high-res shot of the calving fronts of Jakobshavn for April 10?  Appears to be something going on there, looking at EOSDIS (looks too big to be a cloud's shadow):

Thank you Tea Light, must be a cloud after all!

Did you mean the 9th April like your link? The dark blob is the shadow of a low cloud. A later date is not yet available.