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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 1200498 times)

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2400 on: March 12, 2022, 10:11:24 AM »
Jakobshavn Isbræ Update:

Strange behaviour? Looks like very soft ice?

Please click on image to enlarge and animate!
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FredBear

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2401 on: March 12, 2022, 11:27:14 AM »
Quick comment: Lighting is quite different on the two images - from the south in 2021, west in 2022? Changes the textures that can be seen in different areas?
In the textures I see cliff collapse this year at the sides of the north arm but cliff building on the north side of the southern arm - with the ice flow texture of the southern arm flowing out into the fjord (no big icebergs recently).

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2402 on: March 18, 2022, 07:03:56 PM »
Three frames just to look at movement on the north flank of the south branch

grixm

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2403 on: March 20, 2022, 10:19:30 PM »
It begins

Mr. Ä

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2404 on: March 22, 2022, 10:59:42 AM »
I wonder how thick the ice sheet is between the branches. There should be some peaks that are above sea level there right next to the fast moving icestream and I wonder how many years until those peaks are out in the open. There has been alot of new ground visible on the southern side these last few years.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2405 on: March 29, 2022, 10:18:44 AM »
17:03 through 27:03 showing much movement.

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2406 on: March 29, 2022, 03:44:48 PM »
Another large calving as well.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2407 on: May 11, 2022, 04:19:43 PM »
A calving of the southern branch since 08:05 quite big but with what appear to be real giants among the bergs released, see polarview.
A clear day on Sentinel shows, once again, that I can't read Polarview images reliably, big calving shows the 'egg shaped' outbreak as polarview but no 'real giant' bergs, though there's still turbulence amongst the resulting melange.
« Last Edit: May 12, 2022, 11:54:12 PM by johnm33 »

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2408 on: May 27, 2022, 10:44:12 AM »
Jakobshavn Isbræ:

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Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2409 on: May 27, 2022, 03:34:25 PM »
Impressive calving.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2410 on: June 09, 2022, 04:19:01 PM »
02:06 through 08:06 some calving some advance some retreat.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2411 on: June 16, 2022, 11:09:09 PM »
08:06 and 15:06 from click click more calving and if you go to the link it seems some of the bergs are getting caught up on the exit cill.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2412 on: June 29, 2022, 02:13:15 AM »
-50 years
1972 and 1973

Landsat 1-5 MSS L1
Normalised difference water index: (B01-B04)/(B01+B04)
« Last Edit: June 29, 2022, 02:34:30 AM by Often Distant »
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johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2413 on: June 30, 2022, 10:38:55 AM »
15:06 and 28:06 a look at the whole fjord

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2414 on: July 20, 2022, 09:58:14 PM »
3-10-17:07 flow continues, no great advance or retreat but calving proceeds I guesstimate 3km3 of ice in a fortnight. The northern flank of the southern branch seems a little more fluid but so far as I can tell no great outbreak of meltwater so far, that said with consistent movement one supposes any blockages could erode quickly once weakened.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2415 on: July 29, 2022, 10:29:10 AM »
Same dates but 28:07 added, lots of calving little retreat suggests a more fluid glacier, that could also be said of the north face of the southern branch. The lack of ice penetration into the southern branches of the fjord may mean positive pressure from melt.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2416 on: August 16, 2022, 03:16:30 PM »
1-6-12:08 more calving retreat and advance

Stephan

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2417 on: August 16, 2022, 09:41:28 PM »
Thanks John for keeping us up to date with the frequent calvings.
I wonder about the white stripe west of the calving front that is visible in the animations. Where does it come from? It seems to stay in the same position.
It is too late just to be concerned about Climate Change

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2418 on: August 16, 2022, 10:59:41 PM »
Hi Stephan, I suspect that it's where there's a cill and the most recent melange from calving is tightly packed enough to not settle/float until it passes there, but I've been too lazy to actually pull the bathymetry from upthread and check. So it's only a guess.
There's a clear view of Peterman from 14:08 with the sun low in the south giving the profile of that side of the fjord, if you're interested.

Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2419 on: August 17, 2022, 05:01:39 AM »
I wonder about the white stripe west of the calving front that is visible in the animations. Where does it come from? It seems to stay in the same position.

That's just an image artifact of the Sentinel 2 Level 2A processing. If you switch to Level 1C the stripe vanishes.

Level 2A is an enhanced contrast image with colors matching more what you see on the ground with your own eyes.
Level1C is what you see from orbit through the entire atmosphere.

The atmospheric correction formula was made in 2016 or so. So the stripe is just the calving front from whatever date was used as reference to create this formula.

Long shadows also look horrible in the Arctic with L2A. The southern cliffs of the Petermann fjord have abrupt color changes from dark to bright in L2A images.

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2420 on: August 17, 2022, 07:16:59 AM »
Thank you Tealight! I always thought it was some leftover image artifact, as it didn't make sense physically and was not present in some users' animations, but had no clue how to research that.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2421 on: September 03, 2022, 10:55:05 AM »
August 1-6-12-19-27 plus Sept 1, in the last frame the arc has disappeared so assuming Tealights correct, I do, then someones fixed it.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2422 on: October 02, 2022, 03:19:23 PM »
At last another day clear enough to see link
Missed the 25th as a clear day so a gif showing substantial calving in the last week
« Last Edit: October 02, 2022, 07:37:36 PM by johnm33 »

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2423 on: November 06, 2022, 01:11:44 PM »
Jakobshavn Isbræ a busy week in July 1985:

Several massive tabular icebergs are seen in the fjord, some + 2 km2 in area, no wonder the various Ice Services were busy at that time.
The image is composed from data collected from 2 different dates July 2 and 9 1985.
I was by the way involved in the construction of the "new" airport terminal at that time. The airport is located left near the ocean upper part of the image.

Click on image to enlarge. Very large!
Have a ice day!

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2424 on: November 06, 2022, 03:22:05 PM »
Thank you Espen, for both the ice history and personal story.

grixm

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2425 on: February 24, 2023, 10:29:37 AM »
Not sure if this is common at this time of year but Jakobshavn (and Greenland in general) is seeing huge temperature variations in the next few days. From +4 C to - 25 C back to +7 C in just four days. Maybe the glacier will react?

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2426 on: February 25, 2023, 12:21:08 PM »
Welcome to a new season of Sentinel 2 data:
Have a ice day!

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2427 on: February 25, 2023, 03:20:24 PM »
JH calving front location seems to be quite stabilized in the last few years, not gradualy receding as it used to do in the years prior.
I wonder when this situation might change.

A-Team

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2428 on: February 26, 2023, 12:12:57 PM »
Quote
I wonder when this stable situation might change
Indeed, there has not been a progressive retreat of the front the last ten years; calving continues but more or less in balance with the glacial ice moving down the hill.

The big retreat years involve buttressing melange melting away early and high melt inflow upstream. However fundamental changes are often attributed to warming ocean water eating away at the base.

The S2 imagery Espen provided has a slight tint to it, perhaps because it is low angle early season. Splitting the initial RGB into 3 grayscale channels and comparing by differencing, it appears that the red channel alone has better quality than the full RGB.

The question is, do the green and blue channels somehow carry additional information about the ice below and if so, what.
« Last Edit: February 26, 2023, 05:40:19 PM by A-Team »

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2429 on: March 15, 2023, 02:41:30 PM »
There's a persistent brighter arc upstream of the calving front, could this be a building 'wave' backing up from the cill below the front? there's no corresponding shadow. If the whole area++ calves around the 21st I shall assume that's what it was, and that it implies the whole glacier, after the bend, is more like a coherent melange below sea level.
Sentinel

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2430 on: March 16, 2023, 12:15:35 PM »
There's a persistent brighter arc upstream of the calving front, could this be a building 'wave' backing up from the cill below the front? there's no corresponding shadow. If the whole area++ calves around the 21st I shall assume that's what it was, and that it implies the whole glacier, after the bend, is more like a coherent melange below sea level.
Sentinel

If you mean this thing, then that's just an image artifact, a remnant of some post-processing done when the calving front was in that location. You see it on many other glaciers as well.
It is only a problem on Sentinel-2 L2A. Click on "Show L1C" instead.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2431 on: May 30, 2023, 10:25:24 PM »
Finally a clear day sentinel at least two calvings under cloud cover and the melange is mobile perhaps enough to shift and allow a calving around the coming full moon/high tides that could be big given the general melt in the area.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2432 on: June 10, 2023, 09:33:31 PM »
A clear day on 08:06

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2433 on: July 04, 2023, 11:53:44 AM »
Another clear day https://sentinelshare.page.link/JPeQ    02:07

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2434 on: July 10, 2023, 11:36:47 PM »
Courtesy of sentinel another clear day.
Quote
I wonder when this situation might change.
Maybe it's just temporary but it seems there are fewer giants being calved, since I believe these are an impediment to flow over the next upstream cill I anticipate some increase in flow rate.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2435 on: July 15, 2023, 11:34:33 AM »
This image illustrates my point above, I interpret black features of icebergs as ice there's a dearth of those here, it's not that they're not ice but mostly the giants roll over once calved exposing a smoothed surface, hence black. Making use of the artifact mentioned above, which just happens to be above a cill, we can see the retreat is about halfway to the next cill, so I'm guessing in the next few tidal cycles we'll see enough melt/lift[?] to raise a giant ot two over it.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2436 on: July 29, 2023, 11:04:05 AM »
3 images from polarview V.A.K. mentioned how cold Disko was
It looks like two calvings major have taken place beneath cloud cover the first covers the run of the fjord, the second a closer look at the bergs, the last what I percieve as standing waves in the ice caused by an underlying strata that's saturated and where deep bass harmonics impose order on the ice above, I suspect if the terrain was flat we'd see flow.
Definitely need to click the last image then click again to see this, I guess a test would be to align this with the terrain and see if the more pronounced 'waves' match the lows.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2437 on: September 17, 2023, 11:44:32 AM »
A couple of screenshots one which shows the front and it's recent calving and one from upstream showing the circular feature and apparent standing waves in the ice which suggest a liquid base.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2438 on: September 29, 2023, 12:58:15 AM »
A long gif spanning most years from 1975 to 2023. The image quality is nowhere close to spectacular. Perhaps the most interesting thing it shows is the edge of the surrounding Greenland ice sheet receding inland through mass loss.
Climate change is exploited and exacerbated for unsustainable motor nuisance scooters and bikes to block street access across most cities. It only ever gets worse. Heavier than people. Wider than footpaths. Carelessly declared child toys in NZ. Terminable batteries explode toxic emissions on expiry.

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2439 on: September 29, 2023, 06:11:12 AM »
Thanks for the retrospective.

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2440 on: October 30, 2023, 10:51:12 PM »
7 years, 7 images. The glacier isn't very visible, but it's quite an interesting visual of surrounding continental ice movement.
Climate change is exploited and exacerbated for unsustainable motor nuisance scooters and bikes to block street access across most cities. It only ever gets worse. Heavier than people. Wider than footpaths. Carelessly declared child toys in NZ. Terminable batteries explode toxic emissions on expiry.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2441 on: December 03, 2023, 03:53:20 AM »
An up to date animation running throughout the length of one full year. Active calving all along. The fjord is clearing deeper ongoing into December. No off season.
Climate change is exploited and exacerbated for unsustainable motor nuisance scooters and bikes to block street access across most cities. It only ever gets worse. Heavier than people. Wider than footpaths. Carelessly declared child toys in NZ. Terminable batteries explode toxic emissions on expiry.

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2442 on: December 03, 2023, 08:30:34 AM »
Thanks for that animation of Jacobshawn.

sidd