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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 793345 times)

prokaryotes

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2100 on: June 20, 2019, 04:32:21 PM »
An interesting article on the OMG project from the Nasa Earth Observatory.

Turns out the glacier is getting thicker...
My guess...

This anomaly, the Cold blob (North Atlantic) https://en.wikipedia.org/wiki/Cold_blob_(North_Atlantic) … It appears possibly related to global warming-induced melting of the Greenland ice sheet. Which suggest that at least it has a slight negative feedback on marine terminating glaciers. https://twitter.com/climatestate/status/1141083224074084353
CLIMATE STATE WEBSITE | YOUTUBE | USCREEN

Alphabet Hotel

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2102 on: July 01, 2019, 06:04:42 AM »
Another calving event between June 26 and June 29. Click to play.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2103 on: July 04, 2019, 03:32:03 AM »
Large calving between June 30 and July 3. Because the June 29 and June 30 images were obscured by clouds and the previous event was fairly minor, I combined them in this video, which shows the difference between June 26 and July 3.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2104 on: July 04, 2019, 10:23:38 AM »
I woke up thinking about my contrary view of whats happening here, so in this image , which expands with a click, there's a cill at A0 which is about 700m bsl and I'm guessing would sustain an ice wall at 700/9 so 80m/270ft above sea level +/- whatever crushing load and resistance to it the ice brings. At the bend of the southern branch the trough reaches 1400m deep so if bouyant the ice would sustain 160m/540ft of ice +/- same variables. Moving towards the now calving front those variables would be expressed, and where it meets the rising ground the glacier would break as a wave front more or less at the yellow line just as a wave breaks onto a shore. I'm suggesting that the increasing depth of the ice at the calving front indicates that the base has melted out beneath it and further that once that depth reaches equilibrium then the energy that has gone into melting the deep ice will spread not just upstream but sideways into the ice sheet. It may be a good idea to watch for developing wave forms downstream of the deepest parts of the trough.

Barthol

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2105 on: July 05, 2019, 03:16:42 AM »
Another calving event happened between july 3 and july 4.
I wonder what the final retreat will be at the end of the melting season.


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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2106 on: July 06, 2019, 01:33:49 AM »
Another calving event happened between july 3 and july 4.
I wonder what the final retreat will be at the end of the melting season.

I didn't have time to make an animation, but here are the raw images.

Barthol

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2107 on: July 06, 2019, 02:23:44 AM »
Another calving event happened between july 3 and july 4.
I wonder what the final retreat will be at the end of the melting season.

I didn't have time to make an animation, but here are the raw images.
I made a an animation of the raw images that you provided.
And I see the same when i tried it yesterday.
The calving event is obvious, but... besides that it looks as if the whole image is shifting a littlebit.
Everything moves a littlebit, Also the bare rocks.

Dietrich

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2108 on: July 09, 2019, 07:31:21 PM »
Looking at Sentinel image from yesterday, Natural color, I was struck by the darkness of the ice surface of the basin around Jakobshavn.   Took a look at prior years for the same date and it's much darker this year for this date.  Cryokinite (sp?)must be going nuts.   Is anybody aware of a resource tracking albedo year over year?  Sentinel doesn't go back to 2012 and it would interesting to compare that standout year.
Thoughts on this darkening impacting melt ponds > Moulins > Glacier speed / Calving?

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2109 on: July 10, 2019, 02:27:13 AM »
Is anybody aware of a resource tracking albedo year over year?
Take a look at http://polarportal.dk/en/greenland/surface-conditions/
There's a link to the latest albedo map. If you copy that link, paste it in a browser, you can the edit it and get previous dates. I couldn't get 2012 though.






Dietrich

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2110 on: July 10, 2019, 02:39:25 PM »
Thank you for the info.  Seems Albedo, like politics, is local.  What seems to be so notable in the Jakob basin this year is moderated slightly when the Island as a whole is considered.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2111 on: July 13, 2019, 10:46:04 PM »
Another calving and an advance between the 9th and 13th. It looks like there was a big burst of water released? I haven't really looked around much yet, but it looks very different from recent events.

click to animate

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2112 on: July 16, 2019, 11:31:46 PM »
Another calving and an advance between the 9th and 13th. It looks like there was a big burst of water released? I haven't really looked around much yet, but it looks very different from recent events.

click to animate
When I compare the 9th with the 16th, (this week), it looks like there was a greater flow of Ice from the Icesheet towards the calving front, than the loss of ice due to calving events. In other words.. the glacler has grown again a littlebit this week. No retreat this week.
But on the last image from the 16th, it looks as there is a calving event In progress.



« Last Edit: July 16, 2019, 11:40:47 PM by Barthol »

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2113 on: July 17, 2019, 11:07:22 AM »
It retreats into a deep channel which I think has lost it's solid ice base, so the ice present is buoyed up by the 1600m depth, as it approaches the cill the base slows more than the surface. Thus when it retreats it speeds up and it calves as it advances to the cill, once there's enough frozen melange in front of the glacier it calves further forward reacting to the resistance. There's so much ice in so many streams all heading in the general direction of the calving front I don't expect much change to it's present behaviour unless the ice in the main channel is ground down and becomes more fluid.
Upstream there's a circular feature which I think is sitting in water which seems to be preconditioning the ice for just that, there are standing waves which have spread out a little from it and though the ice may be moving the standing waves haven't, at least in the last six weeks. Even so it represents a very small fraction of the ice stream.

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2114 on: July 17, 2019, 12:18:27 PM »
Jakobshavn does not appear to be floating but it calves very close or at the grounding-line.

https://www.the-cryosphere.net/12/2087/2018/tc-12-2087-2018.pdf

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2115 on: July 21, 2019, 01:20:34 AM »
Purely by accident, I have acquired this remarkable image of the increase in melting inland in the last four days. It only appears like this at certain zoom levels, with "show date" enabled. I even had to do screen capture instead of generating an image because doing that also made this split screen effect disappear. Processed with GIMP auto white balance.


vox_mundi

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2116 on: July 21, 2019, 02:05:38 AM »
Geoscientists Discover Mechanisms Controlling Greenland Ice Sheet Collapse
https://phys.org/news/2019-07-geoscientists-mechanisms-greenland-ice-sheet.html

In research published in Nature Communications, a group of scientists led by USF Distinguished University Professor Tim Dixon, Ph.D., uncovered a process that can control the "calving" of glaciers.

... "Iceberg calving has been challenging to model," Dixon said. "One of the big unknowns in future sea level rise is how fast Greenland falls apart, and iceberg calving is one of the least understood mechanisms."

... Scientists have long known that mélange can impede glaciers as they move toward the sea, but they haven't had the data to fully understand the phenomenon.

Dixon's team developed a new radar-based approach to precisely measure elevations of the mélange in front of Jakobshavn Glacier , a major outlet glacier on Greenland's west side. Using analytical techniques developed by Xie, the scientists measured the height of the mélange. The scientists found a thick mélange wedge pressed up against the glacier in late spring and early summer.

During this period, no icebergs calved, the scientists observed. Once the wedge thinned and melted by mid-summer, calving began in earnest.

"On the surface, this mélange is a subtle thing—it appears almost flat- but underwater, there are huge variations," Dixon said. "It's really the underwater part that is pinning the glacier back and preventing it from calving. By precisely measuring the surface elevations, we were able to get a handle on the much bigger sub-surface variations, which define mélange thickness."
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oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2117 on: July 21, 2019, 07:38:33 AM »
Interesting. I have had this theory about Zachariae Isstrom that the sea ice and melange in the enclosed bay impedes calving, and that the clearing of the bay every couple of years in August can speed it up. Turns out the effect of sea ice/melange is verified in Jakobshavn by this research, even though the bay at JH is relatively open.

vox_mundi

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2118 on: July 21, 2019, 08:45:58 AM »
Open Access: Dixon, T., et.al., Rapid iceberg calving following removal of tightly packed pro-glacial mélange
https://www.nature.com/articles/s41467-019-10908-4
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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2119 on: July 22, 2019, 07:56:16 AM »
I've been looking at these 3D glacier bed maps lately. These are the best I can find that show the upper part of the glacier.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2120 on: July 22, 2019, 11:21:23 AM »
Alphabet Hotel. Yes they're the best I've found too, seeing your image of the upstream feature I realised I'd missed the lines forming a little further upstream by the bow lake/melt pond, but now see there are faint lines even further up. I suspect, if my guess about this is right that the area will slowly level out, or slump to 'echo' the contours beneath.

Is there another possible explanation other than the glacier is grounded in water?
vox_mundi, interesting read thanks, looking at the animations it seems there's a breakout of water from the north side sometimes independent of any other action, sometimes precipitating a calving, which may explain the huge discharges into Disko which otherwise have no apparent cause.
nukefix. "Jakobshavn does not appear to be floating but it calves very close or at the grounding-line." agreed but that does not exclude saline penetration of the stream in it's turbulent movment towards the calving allowing all voids created to fill with water at up to 100bar.

Alphabet Hotel

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2121 on: July 22, 2019, 06:18:52 PM »
The entire glacier could be slumping toward the exit, all the way up to where those lines are showing. I don't think that requires it to be floating on water, though. Mass removal from the end like the calvings that happened recently will cause the whole thing to shift downward. Also, the extreme melting be could causing this independently of whether the glacier is moving.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2122 on: July 22, 2019, 06:57:08 PM »
Until the calving front drops below 80m high I won't believe it's floating, but like a no fines concrete it will be porous and the voids full of water below sea level.

 My guess is the slumping will mosty be into the main channel, squeezing any water there out and up, which is the probable cause of the build up upstream.

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2123 on: July 22, 2019, 09:52:06 PM »
Glacial ice acts like a viscous fluid under pressure, not like a bunch of boulders. That being said there are channels that are enable meltwater to move towards lower pressure. I guess there could be some borehole studies of Jakobshavn but I haven't looked.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2124 on: July 23, 2019, 03:37:50 AM »
This is the latest clear image of the upstream area where the melting is happening on the main channel. I think this could be improved, but it does bring out some pretty good detail as-is.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2125 on: July 23, 2019, 03:56:02 AM »
I think the "circular" melt formation I just posted corresponds to this area on one of the 3D maps I posted earlier.

mabarnes

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2126 on: July 23, 2019, 05:00:16 AM »
Apparently this glacier is given to variation in its transport of ice to the coast.  Could it be just "fits and starts" of the flow?  I don't remember where I found this image but as I recall it's from a study of the height of the glacier "upstream." 

Maybe it's built up more "headwaters" and is changing its rate of flow?  I'm curious ... I have no expertise in this area.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2127 on: July 23, 2019, 10:06:46 AM »
My guess

Either way it'll be interesting to see if the wave forms extend into the ice sheet in this extraordinary Greenland melt season.

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2128 on: July 23, 2019, 10:22:55 AM »
Lakes of meltwater form on the surface of the glacier when there's a suitable surface depression that can contain the water. It does not imply there's a lake at the bottom of the ice sheet at the same location.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2129 on: July 23, 2019, 10:01:25 PM »
Alphabet Hotel...

Thank you for this. I love it when we can tease out the detail and relationship between the ice shelf surface and underlying topography. I believe what you are showing is the way that remnant ice caps occur after ice shelf retreat.

grixm

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2130 on: August 05, 2019, 08:03:11 PM »
A calving? Today's view is not available on sentinel yet, but on worldview it looks like it:


Barthol

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2131 on: August 06, 2019, 12:51:42 AM »
Aug 3  and  Aug 5


oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2132 on: August 06, 2019, 02:52:00 AM »
JH is very active this year. I bet it is accelerating like it did in 2012, due to all the meltwater on the ice sheet.

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2133 on: August 06, 2019, 10:13:18 AM »
JH is very active this year. I bet it is accelerating like it did in 2012, due to all the meltwater on the ice sheet.

A question from ignorance: Jakobshavn obviously drains a large part of the Greenland ice-sheet of ice. Does the glacial channel also have the same function for meltwater?

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2134 on: August 06, 2019, 10:44:23 AM »
Good question to which I don't know the answer, although it is reasonable to assume that in general meltwater would gravitate to the lower parts of the bedrock and/or of the ice surface, both of which are in the glacial channel. But meltwater usually drains into moulins, and could take any number of circuitous paths until they emerge somewhere.

Here's some image of the underlying topography:



https://blogs.egu.eu/divisions/cr/2016/06/24/image-of-the-week-canyons-under-the-greenland-ice-sheet/

And some more:





« Last Edit: August 06, 2019, 12:35:29 PM by oren »

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2135 on: August 22, 2019, 10:34:15 AM »
NASA SVS has made these visualisations of simulated futures of Jakobshavn Isbrae until year 2300:

   [RCP 2.6]
  [RCP 4.5]
[RCP 8.5]

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2136 on: August 22, 2019, 11:10:55 AM »
NASA also added the same kind of animation Petermann/Humboldt
Have a ice day!

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2137 on: August 22, 2019, 11:14:25 AM »
The animations seem to disregard changes in local sea-level caused by global mean sea level rise, bedrock rebound and changes in the geoid. It would be super interesting to see simulations of those too..

longwalks1

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2138 on: August 22, 2019, 06:53:13 PM »
Minor quibble, actually sea level change,  Mitrovica et al.  But yes, not factoring in those things is too facile a model. 

Darvince

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2139 on: August 22, 2019, 10:25:02 PM »
Fantastic! More videos showing the simulations of ice sheet melting that undoubtedly are computed often in the scientific literature are very appreciated.

petm

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2140 on: August 22, 2019, 11:28:03 PM »
Very cool

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2141 on: August 27, 2019, 12:48:56 PM »
Another sunny day:
Have a ice day!

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2142 on: September 18, 2019, 11:14:48 AM »
Detail from courtesy polarview


Looking at the north side of the southern calving front, the overturning wave has collapsed. Look at AH post third from top above.