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Author Topic: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland  (Read 254583 times)

budmantis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #750 on: September 03, 2016, 06:47:58 AM »
That huge floe that's been sitting right out in the road off Zachariae Isstrom---that's got a big crack right running north-south now. Compare Aug 21 and Sept 1.

http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698


I could be wrong, but I think its parallel with the 79 degree north latitude glacier. One glacier north of ZI. I've been watching this area with interest for quite some time. I'm wondering whether that last piece of fast ice will break apart before the end of the melt season. Speaking for myself, I've never seen it this fragmented.

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #751 on: September 03, 2016, 12:42:42 PM »
on worldview it is very easy to scroll back to previous years (back to 2013) for comparison
http://go.nasa.gov/2c9hic8
There was just a small piece which stayed fixed on the shallow bank and a small island, Tobias Oer which Espen told us about back then

Cate

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #752 on: September 03, 2016, 01:01:39 PM »
That huge floe that's been sitting right out in the road off Zachariae Isstrom---that's got a big crack right running north-south now. Compare Aug 21 and Sept 1.

http://www.arctic.io/explorer/4Xa5A/2016-09-01/9-N79.19674-W16.60698


I could be wrong, but I think its parallel with the 79 degree north latitude glacier. One glacier north of ZI. I've been watching this area with interest for quite some time. I'm wondering whether that last piece of fast ice will break apart before the end of the melt season. Speaking for myself, I've never seen it this fragmented.


budmantis, yes, thank you for the clarification. It's the glacier/area Andreas T and Wipneus were discussing just a few posts up.

Tealight

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #753 on: September 05, 2016, 02:56:09 AM »
The sun is finally low and I'm able to measure the height of icebergs.

On 3rd September Sentinel 2A captured Zachariae Isstrøm with a solar zenith angle of 72.77 degrees. (17.22 degrees above the horizon) The shadow length of icebergs varies between 100m and 180m giving a height of 31-55m above sea level. The 55m should be seen as the maximum of distinguisable peaks. On average the highest icebergs are more in the 40m range. Assuming a tabular berg and 90% of the mass underwater the total height is 310-550m

See attached image for some measurements.

For the iceberg with the green arrow I calculated the following:
Height: 330m
Area: 1.7795 km2
Volume: 0.587 km3
Mass   : 0.528 Gt
« Last Edit: September 05, 2016, 03:07:15 AM by Tealight »

budmantis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #754 on: September 05, 2016, 06:10:37 AM »
Tealight:

What do you think is the margin of error, if any in your calculations?

Tealight

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #755 on: September 05, 2016, 12:11:05 PM »
Tealight:

What do you think is the margin of error, if any in your calculations?

I rate my shadow length measurement accuracy at around 90%. The area measurement should be over 98% accurate. The polygon drawing tool in SNAP is very precise.

The resolution is 10m and if I'm off by one pixel at 100-180m long shadows the error is 10-5.5%
I also selected edges perpendicular to the incoming solar radiation to keep my angular deviation small. The biggest uncertainty is the surface topography of icebergs, which is hard to estimate with a top down view. The restriction to only being able to measure one edge makes it even harder.

One iceberg had its ripples(perpendicular to the glacier flow direction) alligned with the solar azimuth angle and created a distinct shadow. Its the best example to show the surface height uncertainty. (pictured)
« Last Edit: September 05, 2016, 12:47:32 PM by Tealight »


Cate

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #757 on: September 07, 2016, 11:57:15 AM »
That massive floe sitting off the 79N glacier, discussed above #752 etc---in pieces now, and moving apart. 

Jim Hunt

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #758 on: September 07, 2016, 07:39:13 PM »
That massive floe sitting off the 79N glacier, discussed above #752 etc---in pieces now, and moving apart.

Thanks for the heads up Cate. A nice clear day today!
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #759 on: September 07, 2016, 11:17:26 PM »
Seems like somethings worth a closer look than I can manage.

I'm not sure what you were referring to with this Sep 5 image, but here's an animation between Sep 3 and Sep 5. Only thing I can see is the sea ice breaking again and some rotational movement of the bay, with a few clouds at the top of the image.
I know it's not so smooth and only b&w, but hey at least I managed to make a crude animation after a long while.
(must click)

budmantis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #760 on: September 08, 2016, 01:34:32 AM »
That massive floe sitting off the 79N glacier, discussed above #752 etc---in pieces now, and moving apart.

What remains of the main floe must be anchored to a small island and/or very shallow water. Looking over the images of the last three days, it doesn't appear to be moving. Seems likely there will be more pieces breaking off in the next few days.


Cate

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #761 on: September 08, 2016, 04:12:31 AM »
budmantis, yes, Andreas T mentions this in post #751 above. It does look grounded there, and everything else around it on the move.

budmantis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #762 on: September 08, 2016, 06:01:42 AM »
budmantis, yes, Andreas T mentions this in post #751 above. It does look grounded there, and everything else around it on the move.

Thanks for reminding me, I had forgotten about that post. Andreas's graphic from 2013 shows that area as being more fragmented than it is this year. What is left of most of that fast ice is still in the vicinity and will likely congeal as the re-freeze takes hold. In a way that is good, we'll be able to talk about it next year!

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #763 on: September 08, 2016, 12:00:55 PM »
Thanks Oren you put it centre stage, I thought the cracks appeared to be extending across a much wider front than usual, there normally being several calving streams. In close up it appears just chance that the various streams cracks are aligned.

dingojoe

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #764 on: September 13, 2016, 12:24:51 AM »
Longtime watcher, rare time poster

Would love a clear shot of this area before the season ends as it looks like there was a mass implosion of the ice in this area.  You get used to watching the breakup of ice along here into big white blocks of ice that dance around and eventually break into smaller blocks or even implode into what looks like, from our satellite view, as powdery ice which will then swirl around in Vincent Van Gogh Starry Nights fashion before melting out. 

It seems that a storm brought strong easterly winds and ultimately snow to the area, but it also looks like virtually all of the blocky white ice (except maybe a core of the fast ice that lives well offshore)  imploded en masse in the past week.   Granted it's only been a few years that we have the kind of technology to view this, but I've never seen an event that quite rivals this.

Cate

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #765 on: September 13, 2016, 02:56:48 AM »
dingojoe, great comparison, ice swirling like Starry Nights. Perfect. I am new to watching the ice and it's hard to know what's normal and what's anomalous, so I do appreciate the context you bring from previous seasons--thank you.

Iceismylife

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #766 on: September 13, 2016, 04:00:38 AM »
It broke up in 2013.

http://go.nasa.gov/2cSOMcP

But it is not normal.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #767 on: September 13, 2016, 08:36:07 PM »
Several Danish newspaper are spreading a "canard" involving Jason Box, claiming Spaltgletscher calved, which did not happen, as usual papers gets all the facts wrong:

http://www.b.dk/nationalt/isflage-river-sig-loes-efter-groenlandsk-varmerekord

http://jyllands-posten.dk/indland/trafik/ECE8999622/gigantisk-groenlandsk-isflage-har-revet-sig-loes-efter-varmerekord/
Have a ice day!

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #768 on: September 13, 2016, 10:27:34 PM »
#759

The images were not correctly aligned to fixed rock, distorting motion. On these too-dark images, simply hit the 'auto' button within contrast correction -- it makes a huge difference.

They released a Sep 13, 2016 youtube showing 4 Landsat-8 stills, not worth watching.
https://www.youtube.com/watch?v=QzKTIgRW-j8

Master's student Karina Hansen alerted glaciology Prof. Jason Box of GEUS, "something looks strange" at Spalte (Split) Glacier.

The ~9 km wide Spalte Glacier is a tributary of the 79 Glacier which today has the Arctic's largest ice shelf. The ice shelf forms the end of the North East Greenland Ice Stream, the only Greenland ice stream clearly reaching the highest elevations.

We observed that between 14 Aug 2015 and 3 Sept 2016 a marine-terminating tributary of the 79 fjord glacier, the Spalte Glacier flowing into Dijmphna Sound has detached and area (more than 95 km2) roughly the area of Manhattan.

The detachment of the ice shelf fragment appears to be nearly 100% complete. But the fragment has not floated away yet.


September 13, 2016 A gigantic piece of ice the size of Manhattan has broken away from a glacier in northeast Greenland. Summer Heat in September occur frequently A gigantic block of ice of more than 95 square kilometers - equivalent to an area the size of Manhattan - has broken away from a glacier in Northeast Greenland. Measurements from 14 weather stations in Greenland are reporting temperatures in 2016 are much higher than they used to be, figures from the Danish Meteorological Institute (DMI).

Floe that has come loose, is one of the consequences of this year's heat record. So says Jason Box, research professor at the Geological Survey of Denmark and Greenland. The hot temperatures is one of the reasons that the floe has broken loose from the glacier, he said. When the ice melts on a glacier, water seeps into cracks in the surface. It has the strength to tear the ice sheet from each other, he explains and points out that other factors also play a role. My guess is that there is melted more ice on Greenland this year than there has been for the past three years, says the professor.

Floe has broken loose from fjordgletsjeren gap that lies outside of the weather station Denmark Port in northeast Greenland. Here arises the monitoring stations also heat record this year.

According to the professor, the high temperatures on the island have major consequences. I think we will see more glaciers will crack on Greenland in the future as a consequence of these drastic temperature increases. The heat is going to affect the ice will continue to melt, but it can go faster now, says the professor.

Floe has not yet moved away from the glacier, but according to Jason Box will glacier float away later in the year if it is not already. Recent satellite images we have received is from September 3, so it will be interesting to see how it looks, the next time they come, he says. Floe seems to be broken into more than a piece already

http://www.b.dk/nationalt/isflage-river-sig-loes-efter-groenlandsk-varmerekord
.
« Last Edit: September 13, 2016, 10:52:46 PM by A-Team »

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #769 on: September 13, 2016, 11:32:30 PM »
#759
The images were not correctly aligned to fixed rock, distorting motion.
I know, I kind-of-aligned them manually on a slow laptop which was quite difficult.

Tealight

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #770 on: September 14, 2016, 12:46:06 AM »
We observed that between 14 Aug 2015 and 3 Sept 2016 a marine-terminating tributary of the 79 fjord glacier, the Spalte Glacier flowing into Dijmphna Sound has detached and area (more than 95 km2) roughly the area of Manhattan.

There is virtually no calving progress between these days. What kind of satellite images have they looked at?

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #771 on: September 14, 2016, 05:20:38 AM »
I wonder how Jason Box got involved in that "story"?
Have a ice day!

binntho

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #772 on: September 14, 2016, 07:33:37 AM »
I wonder how Jason Box got involved in that "story"?

In one of the articles in the press today Jason Box is reported as saying that the big chunk hasn't floated away from the glacier yet, but that it will eventually do so.

According to the same report, the latest satellite images they have are from 3rd September, showing the chunk had still not moved away from the glacier. Apparently there is a DMI weather station in the vicinity, but it isn't clear from the article whether they have any direct measurements, possibly a fly-over?

The record temperatures in Greenland this spring and summer are reported in the danish press today, perhaps that has caused some focus on this (potential?) calving, resulting in a bit of premature reporting?

But Jason Cox is quoted directly, saying "The warm temperatures are one of the reasons the icefloe has broken free from the glacier" and "The latest satellite images we have are from the 3rd of September so it will be exciting to see what it looks like the next time".

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #773 on: September 14, 2016, 12:08:00 PM »
Looking now at two 10 m Sentinel 2A of matched geometry (27XWJ UTM zone 27N) dated July 24th (day 206) and Sept 7th (day 251), some widening is indeed seen over the 46 day interval. The images are aligned to fixed rocks on the fjord walls so the later date reflects some glacier advancement as well as fracture widening.

The full resolution gif will require opening separately to animate. Using the known scale there, the crack has bowed out (widened more centrally, cracking and displacing the wedge above) from 149 m to 323 m over the 46 days for an average rate of 3.8 m per day, in addition to an overall bulk displacement (green) of 113 m to the NE.
 
Glaciologist M Pelto wrote about this situation back in June 2013:

The second set of images indicates the change in terminus position at the northeastern terminus from 2000 to 2011, purple dots, often referred to as Spaltegletscher. The yellow arrow indicates a longitudinal rift that has developed since 2000 that is nearly connected to another rift near the margin of 79 Glacier. Espen Olsen at the Arctic Sea Ice Forum has suggested that this is what will lead to this area breaking off.

The orange arrow indicates the same location marking the terminus of the glacier at its northwest corner. The last image is from June 16, 2013 this MODIS image indicates the two rifts red and yellow arrow at the start of the Spaltegletscher terminus. Followed by Landsat image from June 17, 2013 indicating the new terminus position more clearly and the same rifts. Another iceberg has peeled off since 2011, and the total ice loss since 2001 is 70-80 square kilometers.

Jason Box, Ohio State had noted a loss of about 50 square kilometers from 2000 to 2010. Also apparent is an area of active calving and icebergs in front of Zachariae, check out the new icebergs in the June 17, 2013 Landsat at Zachariae Ice Stream

http://blogs.agu.org/fromaglaciersperspective/2013/06/18/nioghalvfjerdsbrae-79-glacier-northeast-greenland/
http://forum.arctic-sea-ice.net/index.php/topic,238.msg4473.html#msg4473 Espen
http://forum.arctic-sea-ice.net/index.php/topic,238.msg7988.html#msg7988 Espen


Lambert Land separates the Inland Ice outlet glaciers of Nioghalvfjerdsbræ and Zachariae Isstrøm just as Hovgaard Ø splits Nioghalvfjerdsbræ into a main stream that flows into Nioghalvfjerdsfjorden and a northern outlet glacier, Spaltegletscher, that flows into Dijmphna Sund. Spaltegletscher is reported to have had a retreat of 18 km between 1907 and the 1950’s and. in spite of the errors in determining the old frontal positions, a major recession of the outlet glaciers must have taken place during the first half of the 20th century [Satellite Image Atlas of Glaciers of the World, 3rd image]
« Last Edit: September 14, 2016, 12:41:31 PM by A-Team »

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #774 on: September 14, 2016, 12:13:40 PM »
The full size animation (needs click) mentioned above has been moved here as it interferes with forum display of other images. This is at 10 m per pixel scale should be used to make measurements of displacements. Overall motion is fairly complex, comprised of glacier advance, coupled displacements of rigid blocks and their rotations about pivot points.We've seen all this before -- but with fewer blocks -- at Petermann Glacier on the other side of Greenland.
« Last Edit: September 14, 2016, 12:58:06 PM by A-Team »

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #775 on: September 14, 2016, 12:46:06 PM »
Superb animation. It definitely looks like an almost-calved situation. I guess SG (Spaltegletscher) is soon to be history. It seems (wild layman guess) that as Zachariae is flowing more easily in the last few years since its separation from its old tongue (and since the sea ice started clearing in August), and perhaps NG (79 Glacier) does the same, there is not enough pressure/flow to feed SG in a significant manner.
If it does disappear completely, this should speed up NG, at least until SG grows back.

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #776 on: September 14, 2016, 01:23:11 PM »
Not so clear what will happen when. The train is leaving the station but winter is setting in, perhaps stopping it in its tracks. Old sutures can be seen in several places. The upper part of SG is also breaking apart as existing fractures widen (not shown).

Below is a close-up of relative motion. The images were compensated for glacier advance, meaning   aligned so as to fix features in the upper left hand corner.
« Last Edit: September 14, 2016, 03:10:26 PM by A-Team »

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #777 on: September 14, 2016, 04:55:59 PM »
But still I am a bit puzzled why this is dramatized? When nothing really happened to Spaltegletscher over the last couple of years??
Have a ice day!

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #778 on: September 14, 2016, 09:19:51 PM »
just something that caught my eye after the recent snowfall are these patches at the edge of the glacier where the snow presumably melted on water / wet ground?
The area marked with W is clearly water but the more earth colored patches (arrows) are very shallow if the are water surfaces

http://go.nasa.gov/2cFrcTi

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #779 on: September 14, 2016, 09:24:35 PM »
sorry should have checked this first: 7-2-1 band shows this to be water on the 7.9.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #780 on: September 14, 2016, 09:25:35 PM »
That is Blåsø (Blue Lake) and a unnamed lake.
Have a ice day!

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #781 on: September 14, 2016, 10:11:19 PM »
nothing really happened

And attributing it to warmer air temperatures in a very cold region in a rather cold year (at least for same-latitude Petermann) ?

If something were to happen -- and it might -- some people would be inclined to attribute it to warmer ocean water circulating under the ice shelf, rather than air or upstream melt (and subsequent glacial acceleration), though that would be secondary discharge circulation of Atlantic Water from Nioghalvfjerdsbræ itself because of a sill, first image below.

Spaltegletscher is quite interesting in how much structural history it exhibits, for example the three splinters on the right side forced by splitting against the protruding rock peninsula and subsequent pivoting about the circular rock island. Right now SG consists of 6-7 rigid bodies. However to decisively unravel the history and forces acting to create and fragment these, it would take a decade or more of satellite record, not just a single season or couple of years.

http://polardispatches.org/measuring-the-flow-of-water-at-nioghalvfjerdsfjorden/

Given that the floating ice tongue of Nioghalvfjerdsfjorden Glacier is one of the very few places in the Arctic where ice and ocean interact at an ice shelf base that covers more than just a very small area, this is a region of particular scientific interest.

We therefore decided to enhance the ice thickness data in this area by using recently obtained airborne radar data as well as 5 seismic soundings and airborne data from 1998.

We used spherical triangulation to interpolated the ice thickness data in the area of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm to our regular grid. The resulting ice thickness map was smoothed along the flow lines to avoid interpolation artefacts. Compared to M-2014, the main benefit of our grid is that it also covers the thickness of floating ice in Dijmphna Sund (Figs. 5c and 5d below).

http://www.earth-syst-sci-data-discuss.net/essd-2016-3/essd-2016-3.pdf 2016 free full


The mass loss at Nioghalvfjerdsbræ is primarily due to rapid submarine melting. Ocean data obtained from beneath the Nioghalvfjerdsbræ ice tongue show that melting is driven by the presence of warm (1°C) Atlantic Intermediate Water (AIW).

A sill prevents AIW from entering the cavity from Dijmphna Sund, requiring that it flow into the cavity via bathymetric channels to the south at a pinned ice front. Comparison of water properties from the cavity, Dijmphna Sund, and the continental shelf support this conclusion.

Overturning circulation rates inferred from observed melt rates and cavity stratification suggest an exchange flow between the cavity and the continental shelf of 38mSv, sufficient to flush cavity waters in under 1 year. These results place upper bounds on the timescales of external variability that can be transmitted to the glacier via the ice tongue cavity.

 http://onlinelibrary.wiley.com/doi/10.1002/2015GL064944/abstract
« Last Edit: September 14, 2016, 10:21:41 PM by A-Team »

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #782 on: September 14, 2016, 10:21:57 PM »
I read somewhere Lake Blaso is tidal, I checked Wiki, wasn't there.

budmantis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #783 on: September 14, 2016, 10:30:17 PM »
Incredible detail and graphics A-Team. Thanks!

skanky

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #784 on: September 14, 2016, 11:00:43 PM »
Here it is from the horse's mouth, as it were:

http://jasonbox.net/news/

dingojoe

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #785 on: September 15, 2016, 06:08:51 PM »
Same area as #758 on 9-15


Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #786 on: September 15, 2016, 08:19:22 PM »
That is something different from 2013. Toggling from terra to aqua on worldview everything which isn't land is moving . And all the ice has disintegrated, there are no large floes, which I think is a sign of thinning.

http://go.nasa.gov/2cIyhCm

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #787 on: September 15, 2016, 10:32:40 PM »
Despite the fact Spaltegletcher did not calve yet, danish media (national tv tonite) continue to report about this non event, this is "black powder" for people like Anthony Watts, Christopher Monckton and Fred Singer, I dont get it??

Proof of no calving at Spaltegletscher September 15 2016:

Have a ice day!

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #788 on: September 16, 2016, 01:27:52 AM »
But still I am a bit puzzled why this is dramatized? When nothing really was analyzed? The original post is here -- it could be deleted or re-written though the press releases cannot:  http://jasonbox.net/news/

Not his high water mark, indeed troubling.

Four Landsat-8 images were 'prepared' by undescribed methods for the dates bouncing around on images on that web page (first animation below). Having 'prepared' thousands of those myself, that already raised a big red flag because accession numbers, Landsat band, zoom, 
UTM zone, sun angle etc etc were not provided though dates of different years differed by as much as a month and a half.

It emerged that 2013 is way out of alignment, 2015 had too much snow cover, 30 m resolution was used in place of 15 m band 8, and pan-sharpening and color were not done. It seems that 2013 and 2014 nadirs lie just across the border in UTM 26X instead of 27X (see Jakobshavn for problems that ensue from that).

Reverse-engineering their dates at EarthExplorer for accessions provides essential metadata,  enables color re-processing at higher resolution, and permits a wider view of up-glacier conditons  -- more reasons why it's considered non-optional to omit accessions even in a popularized scientific context.

     date     accession              path,row, time of day   sunº   azimuth   snow?
2016 Sep 03   LC80080032016247LGN00    8,3   2016:247:14:51   12.2   -150.5   no
2015 Aug 14   LC80100022015226LGN00   10,2   2015:226:15:02   23.2   -151.9   bad
2014 Jul 22   LC80140022014203LGN00   14,2   2014:203:15:27   29.1   -151.7   no
2013 Aug 20   LC80140022013232LGN00   14,2   2013:232:15:29   21.1   -151.2   some

The discussion itself is way off-base: hydrofracturing is off the table, inapplicable to a floating ice shelf whose grounding line (see above map) is ~100 km to the west, as are air temperatures given the lack of surface drainage features on SG. Continuum mechanics (stress, strain etc) is, as its very name suggests, not relevant to fissuring ice, no reason to bring it up. The lack of a rudimentary google search on sub-surface ice cavities, tides and water circulations, bathymetry, and ice thickness (see above cites) is also problematic.

Moving beyond petty ineptitude, the animation makes clear that Spaltegletscher's past, present and future are all about the relative motion of its uncoupling parts.  Like Espen, I too am greatly puzzled but by the absence of co-moving (Lagrangian) coordinates. That's how motion on top of glacial advance, blocks of rotating ice, diffraction by submerged pinning points, warping by Hovgaard Island  is supposed to be dissected.

It's very instructive (and easy) to work out the relative motions of the block. For example, Nioghalvfjerdsfjorden and much of western SG are surprisingly moving in synch despite the suture zones and fractured melange zone along the coast.

The third animation uses 10 m Sentinel 2A 'processed' by contrast adjustment, absolute layer differencing, histogram equalization and white balancing -- all run as auto commands (in all-platform freeware gimp) to allow anyone to reproduce the outcome on these and subsequent S2A images. The forum version had to be posted at 20 m due to dimensional constraints here.

This shows western SG has moved 71.7 m northeasterly while 79N has gone 41.2 m more ENE betwee  July 24th (day 206) and Sept 7th (day 251)  Thus there's an excellent choice here for a  Lagrangian frame of reference (final frame of 4th animation) to simplify relative motions (relative to mere glacier advance) and determine say whether a fracture widens by the top pulling away or the bottom retreating.

There are some very curious changes in compression wavelengths over the broader scene. These are better explored in the large format 10 m version provided in the next post.
« Last Edit: September 16, 2016, 12:24:12 PM by A-Team »

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #789 on: September 16, 2016, 01:31:17 AM »
There are some very curious changes in compression wavelengths over the scene. These are better explored in 10 m version provided ithis post, it requires a click to animate. (If the forum software will cooperate and load more than the first frame ... may have to load them as singles.)
Spaltegletscher is really an interesting ice sheet. The full resolution images are really worth a look. Because the imagery at 10 m is too large for forum animation software, I've expanded the description of processing so that anyone can download the S2A imagery from AWS and re-create the results on a more robust desktop.
« Last Edit: September 16, 2016, 12:28:13 PM by A-Team »

budmantis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #790 on: September 16, 2016, 07:25:11 AM »
I don't understand why SG is considered a glacier unto itself when it looks to me at least to be a distributary of the 79 North glacier.

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #791 on: September 16, 2016, 01:21:23 PM »
SG is a distributary of the 79 North glacier
Right, just a distributary of the 79N ice shelf, but one with an active present and different future. The animation, at 5m, shows crack propagation over the last 46 days. The static image pair is marked up for changes.

The green asterisk shows a bend in a weak westward-draining melt channel used to remove bulk glacier advance from the comparison.

The yellow asterisk suggests the main crack has slowed and turned north, and will not propagate to the western shore freeing (cslving) the SG ice sheet to move out to the Sound.

The red asterisk shows a new more southerly crack propagating rapidly westward. However it may not join up with an existing crack at the suture zone because the orange asterisk indicates it has taken a turn to the north and then east, possibly leading to a small block being created.

This system too shows no sign of propagating to the western rock shore. Some of the blocks at the far north (off-image) may come loose first. These would create medium size tabular icebergs rather than one giant one if the cracks shown here continued westward.

However the lesson from the 2013-2016 series is that events proceed here 'at a glacial pace'. The open water and melange will freeze solid this fall, even as SG continues its bulk motion north. By next melt season, the relationship to pinning points will have changed and new cracks to the south may arise.

Overall though, SG is heading towards disappearance. Like the Petermann ice shelf, pieces will be breaking off much faster than renewed by glacial advance.
« Last Edit: September 16, 2016, 02:14:18 PM by A-Team »

crandles

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #792 on: September 16, 2016, 03:09:24 PM »

The yellow asterisk suggests the main crack has slowed and turned north, and will not propagate to the western shore freeing (cslving) the SG ice sheet to move out to the Sound.


After yellow asterisk, there seems to me to be a suggestion of a turn to WNW then N then WNW again. Is that a developing crack, or just a drainage channel, or something else or nothing at all eg image artefact or random image noise?

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #793 on: September 16, 2016, 04:08:04 PM »
Is that a developing crack, or just a drainage channel, or something else or nothing at all
Not grasping what you mean by 'after' the yellow asterisk, to its immediate right? There are very small drainage channels throughout that follow troughs of compression folds. S2A images have almost no artifacts or background noise as can be seen by cross-correlating separately 3-4x enlarged channels from their posted 10 m resolution.

The animation below shows the rotating ball bearing (weak blue) that is causing the upper right body to pivot to the left (ccw to NW).

The 'force diagram' below shows some progress closing in on what is going on here. It needs a click to see at sufficient resolution. Earlier years are needed still as well as coverage of 79N further west. Another S2A is due tomorrow too.

The most peculiar feature of this ice sheet is the suture zone, the internal fold and the NW shoreline rubble. These must have formed up-glacier (but where and why?) because they are co-moving with the overall ice sheet in the 2013-16 series.
« Last Edit: September 16, 2016, 04:23:25 PM by A-Team »

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #794 on: September 16, 2016, 06:54:09 PM »
Not his high water mark, indeed troubling.

Must be cucumber time?
Have a ice day!

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #795 on: September 17, 2016, 02:24:00 PM »
Must be cucumber time (silly season)?
Maybe Denmark had an internet outage first week of Sept, so they couldn't access EarthExplorer, Google Earth or prior scientific papers?

There's a very interesting story going on with Spaltegletscher but not the one being told. It really has to do with Antarctica where the floating ice shelves are being undermined by warmer ocean waters, not Greenland and warmer air temperatures.

The rapidity with which Spaltegletscher is disintegrating is quite remarkable. To see that, it's a good idea to look at the last 10-15 years of Landsat-7/8 imagery which is available with 10-15 minutes of effort at EarthExplorer.

While the 10 meter Sentinel 2A imagery is a great improvement over Landsat, recall that WorldView satellites have truly fabulous resolution, sub-meter. While proprietary, there's a scientific license and even better, free and immediate availability of back dates at Google Earth if you just click on the clock icon in GE Pro.

The first image below shows ice shelf drainage details in front of the splitting island, the second the fracture tip on 27 July 2013, and the third a fully propagated crack that had not resulted in calving three years later.

The second and fourth image show extensive blue water in what could be termed the central melt channel collector instead of suture zone (as above), though this only raises new questions as to why the ice shelf is lower here, where the water drains, what accounts for the extreme meandering, and why it is not central as at Petermann. The elevated fold, which casts shadows at this high resolution, remains an unexplained oddity as does the point of compression wave refraction.

Here is a 12 year series, to be discussed in a subsequent post. Basically Spaltegletscher is undergoing a rapid and recent collapse, even if it hasn't yet calved. Landsat-7 developed a scan line problem after 2003; EarthExplorer is seriously underwater right now with a ten day delay even for current imagery.

S2A 27XWJ 2016 251 Sept 12 see above posts
LC8008003 2016 247 LGN00 see above posts
S2A 27XWJ 2016 206 July 24 see above posts
LC8010002 2015 226 LGN00 see above posts
LC8014002 2014 203 LGN00 see above posts
WV2......... 2013 208 July 27 see Google Earth       
LC8014002 2013 232 LGN00 see above posts
LE7008003 2012 212 ASN00 band 8 being processed
LE7009002 2011 200 EDC00 band 8 being processed
LE7013002 2010 209 ASN00 band 8 being processed
LE7013002 2009 206 EDC00 preview only
LE7011002 2008 206 ASN00 preview only
LE7007003 2007 223 EDC00 preview only
LE7010002 2006 209 ASN01 preview only
LE7007003 2005 201 EDC00 preview only
LE7006003 2007 248 EDC00 preview only
« Last Edit: September 19, 2016, 12:01:01 AM by A-Team »

prokaryotes

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #796 on: September 17, 2016, 03:56:37 PM »
... this only raises new questions as to why the ice shelf is lower here, where the water drains, what accounts for the extreme meandering, and why it is not central as at Petermann. The elevated fold, which casts shadows at this high resolution, remains an unexplained oddity as does the point of compression wave refraction.


Just googled and seems like it is related to fracturing

2009 study

Englacial drainage systems formed by hydrologically driven crevasse propagation
Recent work has shown that surface-to-bed drainage systems re-form annually on parts of the Greenland ice sheet and some High Arctic glaciers, leading to speed-up events soon after the onset of summer melt. Surface observations and geophysical data indicate that such systems form by hydrologically driven fracture propagation (herein referred to as ‘hydrofracturing’), although little is known about their characteristics. Using speleological techniques, we have explored and surveyed englacial drainage systems formed by hydrofracturing in glaciers in Svalbard, Nepal and Alaska.

In Hansbreen, Svalbard, vertical shafts were followed through 60 m of cold ice and 10 m of temperate basal ice to a subglacial conduit. Deep hydrofracturing occurred at this site due to a combination of extensional ice flow and abundant surface meltwater at a glacier confluence. The englacial drainage systems in Khumbu Glacier, Nepal, and Matanuska Glacier, Alaska, USA, formed in areas of longitudinal compression and transverse extension and consist of vertical slots that plunge down-glacier at angles of 558 or less.

The occurrence of englacial drainages initiated by hydrofracturing in diverse glaciological regimes suggests that it is a very widespread process, and that surface-to-bed drainage can occur wherever high meltwater supply coincides with ice subjected to sufficiently large tensile stresses.

Theoretical considerations indicate that hydrologically driven propagation of surface fractures will occur where a combination of tensile stresses and water pressure is large enough to overcome the fracture toughness of the ice (Ro¨thlisberger and Lang, 1987; Van der Veen, 1998, 2007; Alley and others, 2005).

Surface fractures can penetrate all the way to the glacier bed if water supply is great enough to fill the expanding fracture and offset freezing onto the walls. It has been argued that supraglacial ponds play a crucial role in this process, by providing an elevated head of water at the ice surface (Hagen and others, 1991; Boon and Sharp, 2003; Alley and others, 2005).

Once established, fractures provide high hydraulic conductivity pathways through the glacier, which may then be enlarged into moulins by flowing water. If the fracture or moulin does not completely close during the winter months, it may be reactivated in the following melt season.

https://www.igsoc.org/journal/55/191/j08j038.pdf

2008
Surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change. The process whereby such a pathway is created through thick, cold ice has not, however, been previously observed. We describe the rapid (<2 hours) drainage of a large supraglacial lake down 980 meters through to the bed of the Greenland Ice Sheet initiated by water-driven fracture propagation evolving into moulin flow.

Drainage coincided with increased seismicity, transient acceleration, ice-sheet uplift, and horizontal displacement. Subsidence and deceleration occurred over the subsequent 24 hours. The short-lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially. The integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup.
http://science.sciencemag.org/content/320/5877/778.full
« Last Edit: September 17, 2016, 04:24:09 PM by prokaryotes »

crandles

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #797 on: September 17, 2016, 08:04:41 PM »
Is that a developing crack, or just a drainage channel, or something else or nothing at all
Not grasping what you mean by 'after' the yellow asterisk, to its immediate right?

no left and slightly above. Above lines drawn in below. Hope that is clear now.

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #798 on: September 18, 2016, 11:54:43 PM »
The animation below, which needs a click, adds three more years to the original series. The 2011 is a beauty -- and largely free of the malfunctioning scan lines of Landsat-7. The other two have a different viewing geometry; I have not yet traced down the origin of that.

There has been quite a bit of twitter action in the last few days, with L Dyke posting an animation of lots of 2016 Landsat previews. It isn't in copyable format. https://twitter.com/laurencedyke?lang=fr

DMI posted a S1A radar image of Sept 13th. That picks up the shallow drainage channel -- which is neither a cleft or incipient fracture through the ice shelf -- in the same whitish color as the actual new crack -- but we don't find that misleading because of nukefix has explained that effect several times over at Jakobshavn forum.

LE7008003 2012 212 ASN00 band 8
LE7009002 2011 200 EDC00 band 8 low snow, excellent contrast
LE7013002 2010 209 ASN00 band 8

left of asterisk: crack extension?
No. Not according to the Sept 12th S2A viewed at 2m with strong enhancement (third image). Even if it did, this would not take it anywhere near the shoreline. The crack next door is not a crack but a shallow drainage channel and reaching it would not liberate an iceberg. There should be a return orbit within the next five days; none is posted yet and could be cloudy (like the Sept 17th Landsat LC80100022016261LGN00) or just not taken.

The Landsat-8 for Sept 15th, LC80120022016259LGN00, has some cloud issues ... it is a slow download because of the jam-up at EarthExplorer, only preview below.
« Last Edit: September 19, 2016, 12:22:12 AM by A-Team »

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #799 on: September 19, 2016, 08:33:46 AM »
Probably the last 2016 big calving of Zachariae that we can witness in visible light.

Animation needs a click to start, too big for the 700x700 forum limit.