Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland

[grixm]

Pretty large calving as well. What are the beginning and ending dates for the gif?

March 1st and 5th

[Diaminedave]

Is Jakobshavn appearing to be very active especially for this time of year?

https://worldview.earthdata.nasa.gov/?v=-338353.49881909357,-2347056.703916893,-117733.3479143081,-2213867.501704004&p=arctic&l=Graticule(hidden),Coastlines_15m,VIIRS_SNPP_Brightness_Temp_BandI5_Night(hidden,palette=green_1,min=220.7,max=243.3,squash=true),Reference_Labels_15m(hidden),Reference_Features_15m(hidden),VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor&lg=false&t=2021-04-18-T04%3A00%3A00Z

[johnm33]

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]

April 18th vs 4th.

[Shared Humanity]

Nice calving...mainly breaking up into bergy bits.

[grixm]

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]

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]

BOOM!

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

[sidd]

Bit early, isn't it ?

sidd

[Espen]

A massive calving took place at Jakobshavn between April 30 and May 1 2021.

Please click on image to enlarge and animate!

[johnm33]

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?

[Alphabet Hotel]

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]

Extreme zoom on the bergs from that last calving. Note the scale at bottom right.

[Espen]

Jakobshavn : Another brick in the wall

Please click on image to enlarge and animate!

[nukefix]

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]

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?

[nukefix]

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]

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]

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.

[Espen]

Jakobshavn Isfjord: Still counting - This calving session is unusually long for any time in a season.

Please click on image to enlarge and animate!

[oren]

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]

Here is status of lost / calved ice between April 29 and May 4 2021:

[johnm33]

Thought I'd bump up this bed elevation image again, detail and original

[johnm33]

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

[johnm33]

Still movement, and perhaps more to come soon, 8/10 may

[Alphabet Hotel]

Finally, clear Sentinel images of the latest calving. Had to go back to May 4th to get a clean 'before' image, 'after' is dated May 11.

click to animate

[grixm]

And another one today, it looks like. But sentinel images aren't in yet.

[Linus]

From #2224 above: An interesting feature that is slightly visible in the “before” picture but much more prominently in the “after” picture.

[johnm33]

"Interesting feature" didn't notice it but looking closer it actually moves about 400m between the two shots.
 I have wondered that if the giant icebergs really are blocks released from the depths when they would make their rise to the surface visible, the calving front is above a very deep chasm now and I'm assuming that slowly gets filled with seawater during every full/new moon tidal cycle giving a boost to these rising giants.
Shame no one is sampling these giants with a drone.

[Espen]

Jakobshavn Isfjord - Here we go again, another big one - May 13 and May 14 2021:

Please click on image to enlarge and animate!

[Alphabet Hotel]

There was also a calving event between 11 May and 13 May! (I was wondering where those blocks on the new North Branch had gone.)

Click to animate; click again if needed for 100% zoom

[Espen]

Jakobshavn Isfjord - Another heavy calving happened between May 14 and May 15 2021, sorry for the obscure UFO standard imagery.

[johnm33]

Espen, if you feel inclined, a broader view of the progress of the bergs down the fjord would be much appreciated.

[nukefix]

Big calving confirmed with S1B on 16.5. Judging by the length of the shadow from the calving front the ice cliff is as high or higher than I've ever seen before. Data downloaded from polarview as GeoTIFF and imported to SNAP.

[Tor Bejnar]

As a hard rock geologist (or once-upon-a-time student thereof), I wonder at the lineation circled below.  Is it a 'mega-groove" created by the glacier when it was much thicker or is it associated with the bedrock geology? (A half-hour internet search revealed only that the lineation shows up in different types of imaging.)

[nukefix]

It looks like a physical fracture in the radar image. These must be common in bedrock that has been below substantially more ice during the ice ages(?) - this can be seen in Scandinavia too.

[Stephan]

Just a question:
There have been several major calvings at Jakobshavn in the last weeks. How far is the actual calving front away from its historically highest upstream position?

[Shared Humanity]

As a hard rock geologist (or once-upon-a-time student thereof), I wonder at the lineation circled below.  Is it a 'mega-groove" created by the glacier when it was much thicker or is it associated with the bedrock geology? (A half-hour internet search revealed only that the lineation shows up in different types of imaging.)

No idea but it is cool.

[Espen]

Jakobshavn Isfjord - Another one of them calvings - May 15 - May 16 - 2021

(Sentinel 2 data from May 16 2021 is not worth using)

Please click on image to enlarge and animate!

[HapHazard]

As a hard rock geologist (or once-upon-a-time student thereof), I wonder at the lineation circled below.  Is it a 'mega-groove" created by the glacier when it was much thicker or is it associated with the bedrock geology? (A half-hour internet search revealed only that the lineation shows up in different types of imaging.)

I've no idea at all, but it reminds me of features I've walked on, where glaciers have melted back significantly. Here's 2 pics from my backpacking trip last summer. In the center of the first image you can see a horizontal line halfway up the valley side. 2nd image is taken from a path on that exact spot. A glacier used to fill that valley.

[Tor Bejnar]

Another half-hour found this paper:
Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland

    July 1999Geological Survey of Denmark and Greenland 191

DOI:10.34194/ggub.v181.5108
Authors:
Adam A. Garde
Agnete Steenfelt
    Geological Survey of Denmark and Greenland
full paper PDF

Top image below from an Espen 2013 post  I see a second parallel lineation ~1 km north of the earlier-post circled one.
Bottom image is an extract from the referenced paper (with area of interest circled in red).  The southern edge of the "Supracrustal rocks" on the map does not match either lineation on the ground. (Either they are 'not related' or the map has an error.  I'll presume 'not related' without additional information.  I see a bit of broad  lineation on the image below that matches some of the northern edge of "supracrustal rocks" and a thin one above that.) The following is not a single quote and editorial liberties have been taken...

A description of the Nunatarsuaq domain:  fine-grained, commonly banded [gneissic], light to dark grey biotite-bearing rocks of tonalitic-trondhjemitic composition. Migmatitic appearance and pegmatitic schlieren are common. The gneisses have been folded together with large units of supracrustal rocks which are dominated by metasediment.  Not definite, but some evidence suggests that the orthogneisses intruded the supracrustal rocks.

[gerontocrat]

A new science paper

suggest y'all have a look at "What's New in Greenland"

https://forum.arctic-sea-ice.net/index.php/topic,1090.msg309231.html#new

[Tor Bejnar]

A coastal survey in the southern part of the Palaeoproterozoic Rinkian fold belt, central West Greenland
Article in Geological Survey of Denmark and Greenland · December 2002
DOI: 10.34194/ggub.v191.5109

S. Piazolo,University of Leeds
Kristine Thrane, Geological Survey of Denmark and Greenland

Here is a slightly more detailed geologic map on the area of my interest. See map excerpt with red-circled area below.  The black dashes are shear zones.

It appears a major suture between ancient tectonic plates occurs in Illulissat Fjord (aka Jakobshavn Fjord): The Nagssugtoqidian Belt is to the south and the Rinkian Belt is to the north.

... One of these concerns the boundary zone between the Nagssugtoqidian and Rinkian orogenic belts in central West Greenland (van Gool et al. 2002, this volume, fig. 1). It is quite possible that the two belts formed contemporaneously within a common, or at least related, plate-tectonic setting. However, the structural styles of the two belts are different; ...

This suture zone may be the reason Jakobshavn Glacier formed where it did - a zone of least resistance.

[nukefix]

The granite/gneiss bedrock under the Archipelago Sea is very cracked, I'd imagine because it has been under 2km of ice repeatedly and the elastic and isostatic rebound has cracked it?

[Espen]

Here is one for Johnm33:

Please click on image to enlarge!

[Espen]

Jakobshavn Isfjord:

A lot of action since May 14 2021, notice a new big piece is to leave soon (southern branch).

Please click on image to enlarge and animate!

[Espen]

Jakobshavn Isbræ - Now very close to record retreat - Actually yesterday (May 18 2021) position is  deeper than it was on August 14 2015 before the record calving and retreat August 14 - August 16 2015 https://forum.arctic-sea-ice.net/index.php/topic,154.msg60840.html#msg60840

Please click on image to enlarge and animate!

[oren]

Thank you Espen.
Is it true then that JH is in record retreat for the date? May is quite early for calving so much I think.

[nukefix]

I think Espen meant that the calving front is now receded further than just before the monster calving event in 2015.

[Espen]

Thank you Espen.
Is it true then that JH is in record retreat for the date? May is quite early for calving so much I think.

Yes I am very sure it is, but glaciers like Jakobshavn Isbræ and Zachariae Isstrøm dont really care anymore what time of the year it is, unlike Petermann Gletscher and Ryder Gletscher they need some assistance from the summer "heat".