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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 924064 times)


johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2201 on: April 19, 2021, 03:26:32 PM »
Is Jakobshavn appearing to be very active especially for this time of year?
Not in my opinion, there have been a couple of calvings under cloud cover and the recent new moon tides led to a clear out of the fjord. The only unusual thing I've noticed is a crack/stream south and a little east of the upstream round feature, but after a fairly dramatic appearance it's slowly disappearing into the background.

https://apps.sentinel-hub.com/eo-browser/?zoom=8&lat=69.21915&lng=-50.71289&themeId=DEFAULT-THEME&datasetId=S1_AWS_EW_HHHV&fromTime=2021-04-16T00%3A00%3A00.000Z&toTime=2021-04-16T23%3A59%3A59.999Z&layerId=EW-DH-HH-DECIBEL-GAMMA0&visualizationUrl=https%3A%2F%2Fservices.sentinel-hub.com%2Fogc%2Fwms%2F694b409a-e12b-4922-8d51-c28dc12c8474

grixm

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2202 on: April 19, 2021, 11:37:04 PM »
April 18th vs 4th.

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2203 on: April 19, 2021, 11:55:23 PM »
Nice calving...mainly breaking up into bergy bits.

grixm

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2204 on: April 29, 2021, 11:58:27 PM »
April 24th vs 29th.

Calvings some places, advances other places. Calving fronts have sharpened up nicely. Snowcover on the rocks fading quickly. Sea ice and slush completely dynamic.

Alphabet Hotel

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2205 on: April 30, 2021, 07:15:58 AM »
That stream on the north side of the southern branch seems to be separating and turning into a small separate glacier. Lots of calving there.

Alphabet Hotel

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2206 on: May 02, 2021, 07:38:02 AM »
BOOM!

April 29th - May 1st (2.2 MB GIF)


sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2207 on: May 02, 2021, 08:07:19 AM »
Bit early, isn't it ?

sidd

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2208 on: May 02, 2021, 08:49:33 AM »
A massive calving took place at Jakobshavn between April 30 and May 1 2021.

Please click on image to enlarge and animate!
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johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2209 on: May 02, 2021, 10:50:30 AM »
massive bergs too, probably the full moons tides caused enough melt and gave enough bouyancy to lift those giants over the cill, are there more down there or will we see a rapid retreat for a while?
« Last Edit: May 02, 2021, 10:58:24 AM by johnm33 »

Alphabet Hotel

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2210 on: May 03, 2021, 01:22:49 AM »
The first thing I noticed from this latest event was how far away those large chunks ended up. The last one I remember with bergs this big, they stopped pretty close to the calving front.

I just wish I'd been there to see this one. Must have been a hell of a show. :-)

Alphabet Hotel

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2211 on: May 03, 2021, 08:28:34 AM »
Extreme zoom on the bergs from that last calving. Note the scale at bottom right.


Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2212 on: May 04, 2021, 08:51:50 AM »
Jakobshavn : Another brick in the wall

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nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2213 on: May 04, 2021, 03:05:48 PM »
Interesting to see how the 1st of May image has calved those very deep blue icebergs. I've been told they blue features are refrozen lakes but I wonder if that really is the case. If they are refrozen lake remnants they are travelling deeper in the ice-stream and not on the surface.

ps. Espen what is that shadowy artefact in front of the calving front - is that a base-DEM used for hill-shading?

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2214 on: May 04, 2021, 03:40:33 PM »
Interesting to see how the 1st of May image has calved those very deep blue icebergs. I've been told they blue features are refrozen lakes but I wonder if that really is the case. If they are refrozen lake remnants they are travelling deeper in the ice-stream and not on the surface.

ps. Espen what is that shadowy artefact in front of the calving front - is that a base-DEM used for hill-shading?

Those artefacts in front of the calving front, is something I never noticed before, they are seen this season in front of other glaciers too like Zachariae Isstrøm.
The deep blue ice colors is due to the density of the icebergs, is my call?
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nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2215 on: May 04, 2021, 04:59:28 PM »
Those artefacts in front of the calving front, is something I never noticed before, they are seen this season in front of other glaciers too like Zachariae Isstrøm.

The deep blue ice colors is due to the density of the icebergs, is my call?
Where do you get the image-data from?

The deep blue could be like that since it's a very recent calving, further down the fjord nothing is as blue as in the attached pic.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2216 on: May 04, 2021, 05:14:17 PM »
The artifacts are not visible on playground hub, here or elsewhere, so for now I'm assuming they're something to do with Ecovery. "very deep blue icebergs" The first time these emerged there was a giant that had an upturned keel shape, since which time I've taken them to be deep frozen ice from the base of the fjords eased by tidal water penetration combined with small tidal flexing of the landmass, and still guessing, they're carried downstream beneath a huge overburden of ice, get stuck at the cills and then are released at a time when there's an extreme tidal range.
I underestimated the size of the berg I measured, assuming it to be adjacent to another,

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2217 on: May 04, 2021, 07:21:57 PM »
Those artefacts in front of the calving front, is something I never noticed before, they are seen this season in front of other glaciers too like Zachariae Isstrøm.

The deep blue ice colors is due to the density of the icebergs, is my call?
Where do you get the image-data from? From the ESA Copernicus site.

The deep blue could be like that since it's a very recent calving, further down the fjord nothing is as blue as in the attached pic.
My theory is it similar to black ice with very little air (bubbles) inside resulting in higher density.
Have a ice day!

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2218 on: May 04, 2021, 10:40:10 PM »
Jakobshavn Isfjord: Still counting - This calving session is unusually long for any time in a season.

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oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2219 on: May 04, 2021, 10:46:42 PM »
Very impressive, and not just the main South branch, also the North branch as well as the side flow in the north wall of the South branch.

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2220 on: May 04, 2021, 11:07:08 PM »
Here is status of lost / calved ice between April 29 and May 4 2021:
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johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2221 on: May 05, 2021, 09:14:12 PM »
Thought I'd bump up this bed elevation image again, detail and original

« Last Edit: May 06, 2021, 10:46:46 AM by johnm33 »

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #2222 on: May 07, 2021, 07:59:35 PM »
Interesting paper   about upstream jakobshavn and great selection of images, for instance
Fig. 7. Subglacial water flowpaths for DEMs in Figure 5 with mass conservation topography (a) and the first three geostatistical realizations (b–d). This shows that the main channel is reproduced in each DEM, whereas smaller tributaries vary across realizations. The water routing is superimposed on hillshade topography and plotted on a power 10 scale for visualization.

A-team posted extracts from this a while ago so perhaps a boost for recent members