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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 426776 times)

Oddmonk

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1800 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 #1801 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 #1802 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 #1803 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 #1804 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 #1805 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 #1806 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 #1807 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 #1808 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 #1809 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 #1810 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 #1811 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 #1812 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 #1813 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 #1814 on: February 20, 2017, 08:04:31 PM »
Wondrous!!  Belongs to the Arctic image of the day!!
“You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing -- that's what counts.”
― Richard P. Feynman

Oddmonk

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1815 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 #1816 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 #1817 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 #1818 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 #1819 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 #1820 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 #1821 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 #1822 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 #1823 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 #1824 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/