Support the Arctic Sea Ice Forum and Blog

Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 760938 times)

prokaryotes

  • ASIF Citizen
  • Posts: 191
    • View Profile
    • ClimateState.com
  • Liked: 15
  • Likes Given: 18
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

  • ASIF Citizen
  • Posts: 126
    • View Profile
  • Liked: 51
  • Likes Given: 13

Alphabet Hotel

  • ASIF Citizen
  • Posts: 126
    • View Profile
  • Liked: 51
  • Likes Given: 13
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.

Alphabet Hotel

  • ASIF Citizen
  • Posts: 126
    • View Profile
  • Liked: 51
  • Likes Given: 13
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.

johnm33

  • ASIF Upper Class
  • Posts: 1237
    • View Profile
  • Liked: 52
  • Likes Given: 25
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

  • ASIF Lurker
  • Posts: 9
    • View Profile
  • Liked: 1
  • Likes Given: 1
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.


Alphabet Hotel

  • ASIF Citizen
  • Posts: 126
    • View Profile
  • Liked: 51
  • Likes Given: 13
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

  • ASIF Lurker
  • Posts: 9
    • View Profile
  • Liked: 1
  • Likes Given: 1
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

  • ASIF Lurker
  • Posts: 6
    • View Profile
  • Liked: 1
  • Likes Given: 20
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

  • ASIF Governor
  • Posts: 3928
    • View Profile
  • Liked: 544
  • Likes Given: 1119
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

  • ASIF Lurker
  • Posts: 6
    • View Profile
  • Liked: 1
  • Likes Given: 20
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.

Alphabet Hotel

  • ASIF Citizen
  • Posts: 126
    • View Profile
  • Liked: 51
  • Likes Given: 13
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

Barthol

  • ASIF Lurker
  • Posts: 9
    • View Profile
  • Liked: 1
  • Likes Given: 1
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

  • ASIF Upper Class
  • Posts: 1237
    • View Profile
  • Liked: 52
  • Likes Given: 25
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

  • ASIF Citizen
  • Posts: 440
    • View Profile
  • Liked: 5
  • Likes Given: 1
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

Alphabet Hotel

  • ASIF Citizen
  • Posts: 126
    • View Profile
  • Liked: 51
  • Likes Given: 13
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2115 on: Today at 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

  • ASIF Middle Class
  • Posts: 866
    • View Profile
  • Liked: 146
  • Likes Given: 77
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2116 on: Today at 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."
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

oren

  • ASIF Governor
  • Posts: 3928
    • View Profile
  • Liked: 544
  • Likes Given: 1119
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2117 on: Today at 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

  • ASIF Middle Class
  • Posts: 866
    • View Profile
  • Liked: 146
  • Likes Given: 77
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2118 on: Today at 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
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late