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Author Topic: Zachariae Isstrøm / Nioghalvfjerdsfjorden / NE Greenland  (Read 553006 times)

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #650 on: April 18, 2016, 08:24:37 AM »
Zachariae update. In the first animation the ice can be seen grinding around Kap Zach. On the right side of the images one of the larger icebergs can be seen to split in two.
In the second image the 16 April image was shifted 52x6 pixels to align the images on the left. That translates to a daily movement of 6.54 m. All four visible future calving fronts can be seen expanding.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #651 on: April 18, 2016, 04:39:19 PM »
Wow, nice imagery. The extra umph of Sentinel 2A resolution really makes a difference. And your color pipeline is paying good dividends with these. An interesting technical question, how much better is this than two 30 m Landsat-8 color channels pansharpened to 15 m with band 8. I suppose the comparison to true colors would be to OMG color imagery taken at 13 000 m; however I could not find where they are archiving their gallery of the whole coastline.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #652 on: May 01, 2016, 10:47:09 AM »
(R)evolution: images by Landsat-8 (normal 30m/pixel), Landsat-8 pan-sharpened to 15m/pixels end the Sentinel with a normal 10 m/pixel resolution. Everything scaled to 5m/pix.


oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #653 on: May 01, 2016, 04:03:48 PM »
The Sentinel is soooo much better. The resolution doesn't tell all.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #654 on: May 01, 2016, 10:14:12 PM »
Quote
(R)evolution: images by Landsat-8 (normal 30m/pixel), Landsat-8 pan-sharpened to 15m/pixels end the Sentinel with a normal 10 m/pixel resolution. Everything scaled to 5m/pix.

Nice product. I am curious what such a triple would look like for the Petermann crack tips that we have been monitoring. The S2A may still be fairly decent at 2.5m. I'm still mulling over whether more could be done to use up the three 10m channels to make an even sharper one channel. Seems like there should be some statistical process while still in 16-bit that could reduce noise, maybe just average or the median pixel value of the three.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #656 on: May 10, 2016, 07:06:26 PM »
Among the icebergs, one decides to split.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #657 on: May 11, 2016, 12:17:15 AM »
It's odd that both parts move off in opposite directions. There must have been odd forces involved there, and neither part appears to be grounded.

It doesn't help that it reminds me of Pacman.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #658 on: May 11, 2016, 12:26:46 AM »
It's odd that both parts move off in opposite directions. There must have been odd forces involved there, and neither part appears to be grounded.

It doesn't help that it reminds me of Pacman.

that's the momentum from separation, everything the brakes separates to a certain amount, see it as a braking not just as a simple separation, there was energy that transferred into kinetic energy, has nothing to do with the surroundings.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #659 on: May 11, 2016, 12:36:51 AM »
It's odd that both parts move off in opposite directions. There must have been odd forces involved there, and neither part appears to be grounded.

It doesn't help that it reminds me of Pacman.

>> that's the momentum from separation, everything the brakes separates to a certain amount, see it as a braking not just as a simple separation, there was energy that transferred into kinetic energy, has nothing to do with the surroundings.



To be more precise probably a tilt in the two pieces against each other along the old long axis. Acts a bit like a lever.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #660 on: May 11, 2016, 10:40:03 AM »
On closer inspection it would appear that the lower section has dropped after separation, so I assume the break was caused by the thinner lower part being held up by the top part, and finally snapped off.

Just as Plinius described.  ;)

I still can't lose the Pacman image though.  ::)

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #661 on: May 11, 2016, 03:44:51 PM »
The Zachariae glacier keeps advancing with an undiminished speed of 6-7 m/day. However there are only few and only small events to report. Yet on the long run new cracks can be seen developing.

In the first animation a 40 day difference shows the forming of a new branch in a sort of "Y"-shape (center of the image, Kap Zach is at the bottom-right). The forming of this new branch is easy visible from S1A radar images as well.

This is a gradual process with multiple little steps. One such step can be seen in the second animation with the images less than 24 hours apart. Some part of the top layer collapses, exposing the open crack.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #662 on: May 31, 2016, 12:54:39 PM »
The R025 series (images taken when the Sentinel 2A is in relative orbit #025) has until now delivered only images with few or no clouds. That enables series of two months (6 images 10 days apart).

Here is one of the active southern half (near Kap Zach).

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #663 on: May 31, 2016, 02:38:15 PM »
Very nice series. They seem to be using a zero in RO25 rather than the letter oh so make that 'relative zorbit' maybe?

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #664 on: June 10, 2016, 06:36:41 PM »
Something is broken in the S2A data.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #665 on: June 10, 2016, 08:25:35 PM »
"Something is broken in the S2A data."
Let's hope for a quick fix the fast ice thereabouts is shrinking daily.
added
certainly looks like something is happening to N79
« Last Edit: June 11, 2016, 01:27:48 PM by johnm33 »

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #666 on: June 11, 2016, 01:52:38 PM »
what always surprises me in these animations (see wipneus' post #662) is how uniformly th melange moves with the icebergs. What is the driving mechanism there? The whole lot is moving towards sea ice which has not budged for a couple of years now if I recall correctly. I know there is a circulation of buoyant meltwater from beneath the glacier tongue but I would expect this to be stronger or weaker in places across the width of the glacier.
How much is known about this?
Thanks, Wipneus, for providing these animations.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #667 on: June 11, 2016, 02:18:22 PM »
sea ice which has not budged for a couple of years now
To be accurate, the last time the sea ice cleared was in August 2014, which brought with it a huge retreat and clearing of the icebergs. So this melange definitely plays a role in stabilizing the glacier.
This year I expect the sea ice to clear again due to the warm Atlantic and the low Greenland Sea extent, but we'll see.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #668 on: June 11, 2016, 05:19:53 PM »
thanks oren, that helped me find a suitable reference point, looking over longer periods there is relative movement and distances between icebergs change. I don't know whether the allignment of those two Landsat images is the same but using these rocks as markers I hope I'm fairly consistent
first image from 14.9.2014
And here is my favorite, Zach always impress me, because this is not a "Mickey Mouse" glacier like so many others, and here she come:
second from 8.3.2016
First usable Landsat 8 image from 2016. Here is a pan-sharpened large image at 15 m/pix resolution. ...
I have marked recognizable bergs , spotting the changes with breaking and turning bergs is quite fun

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #669 on: June 18, 2016, 06:24:32 PM »
Looking to the north of Nioghaivfjerdsfjorden [N79] this from the 15th shows a darker area adjacent to the coast which I suspect is reinforced with freshwater melt from the glacier, and a larger lighter more clearly 'marbled' area of ice further out.

[ http://ocean.dmi.dk/arctic/images/MODIS/NEW/20160615s01a.ASAR.jpg ]
and this shows the lighter area detatched and possibly the purple [ish] ice in the fjord just to the north indicates the beggining of warm water penetration beneath the ice which may lead to the loss of the thicker landfast ice.

[ http://ocean.dmi.dk/arctic/images/MODIS/NEW/201606181317.jpg ]

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #670 on: June 18, 2016, 06:32:08 PM »
Possibly some melt occuring just south of Zachariae too

[ http://ocean.dmi.dk/arctic/images/MODIS/Joekelbugt/201606181317.jpg ]
added:- I thought I'd take a closer look at the glaciers so this is a detail from https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c03.2016170.aqua.250m.jpg  I can almost persuade myself that warm water is penetrating as far as the north shore of the fjord containing N79, if that's the case some movement will happen soon.
« Last Edit: June 18, 2016, 07:28:31 PM by johnm33 »

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #671 on: June 19, 2016, 12:27:33 AM »
The appearance of the "marbeled ice" is explained by looking back at last autumn when there was some breaking and movement just before darkness returned to that area.
TERRA 1.10.2015
http://go.nasa.gov/26a2Pj7
IR image when light was too low for visible images:
http://go.nasa.gov/1YyNSEF
worldview makes it much easier than the DMI site to look through other dates and click from visible to near IR (band 7-2-1) and long IR (band31) but of course doesn't have the SAR images.
The very light shades in the open water area in the SAR image are waves as far as I know

The images which show some ice coloured in purple look like the 7-2-1 images but with purple instead of the darker blue indicating water on the ice surface. Can you point to information on these images?
« Last Edit: June 19, 2016, 12:32:36 AM by Andreas T »

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #672 on: June 19, 2016, 04:11:39 PM »
I tweaked this with Gimp to enhance the purple

I've just realised that the fjord north of N79 [with the triangular island] is actually open to the fjord further north still and that the whole complex is about to become distinct islands, which will leave it very vulnerable to erosion from waters pouring out of the arctic. That'll change the whole dynamic for Nioghalfjersfjorden, if it isn't already.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #673 on: June 20, 2016, 05:57:29 PM »
The glacial ice of the Zachariae has become much darker in the last week or so. That is the top of it, where calvings have toppled the ice stays much brighter and the ice melange in between has a color in between.


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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #674 on: June 20, 2016, 11:06:17 PM »
Take a look at the northern side of N79 http://go.nasa.gov/28Ktr5Z then go back to the 12th, http://go.nasa.gov/28Kw2wT  is it possible that the glacier is going to begin calving/discharging into the north channel?

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #675 on: June 23, 2016, 12:47:06 PM »
The "darkening" goes up-glacier and with it the number of melt ponds explodes.
(S2A image scaled to 50m/pix for size).

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #676 on: June 23, 2016, 02:19:48 PM »
Take a look at the northern side of N79 http://go.nasa.gov/28Ktr5Z then go back to the 12th, http://go.nasa.gov/28Kw2wT  is it possible that the glacier is going to begin calving/discharging into the north channel?

This is the "north channel" on June 12 and 22, scaled to 20 m/pix. Nothing beyond a very slow forward movement can be seen. The explosion of melt ponds happened here as well though.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #677 on: June 26, 2016, 10:00:59 PM »
Thanks Wipneus
Looking through the cloud it seems the Greenland sea ice break-up has reached N79

http://go.nasa.gov/296EhBV
It won't be long before these sleeping giants wake

http://go.nasa.gov/29aSwpu
« Last Edit: June 28, 2016, 10:18:21 AM by johnm33 »

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #678 on: June 29, 2016, 02:19:10 PM »
The Zachariae glacier is rather smoothly continuing its advancing glacier fronts, opening cracks, melting further and further inland.

So the most interesting I have here is two calvings splitting in one image.  One calving (the darker one) still upright, the other toppled over. There is a crack developing in the ice melange as well. These events are probably not directly related, the crack in the toppled ice berg happened 4 days before the one in the upright calving and the crack in the melange is still older.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #679 on: June 29, 2016, 06:13:02 PM »
Seems interesting they are all so close to each other. Suggests there is some common root cause. Could it be warm surface water entering the fjord, being drawn in by cold basal melt exiting?

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #680 on: June 30, 2016, 10:58:43 AM »
Seems interesting they are all so close to each other. Suggests there is some common root cause. Could it be warm surface water entering the fjord, being drawn in by cold basal melt exiting?

It is at the edge where the ice melange that is moving with the glacier front is rubbing the ice melange that is fasted to bedrock. My impression is that this is only a smaller contribution to the forces that  make these ice bergs break.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #681 on: June 30, 2016, 11:00:35 AM »
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #682 on: July 03, 2016, 08:41:20 AM »
Small calving near "Kap Zach".

Shared Humanity

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #683 on: July 03, 2016, 03:26:14 PM »
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.

Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #684 on: July 03, 2016, 03:49:54 PM »
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.

Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?

I highly doubt that though I know nothing of the subject. I would assume the melt ponds freeze in winter and melt in summer, and perhaps at some point due to weather they iced over, and now that ice cover melted. Can be checked by looking at LandSat preview images over time in EarthExplorer.

magnamentis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #685 on: July 03, 2016, 07:01:44 PM »
not sure about melt ponds but it's proven fact that under the ice "embedded" are entire lakes that survive winters. i could imagine that once, relatively warm melt water fills a deep enough reservoir and that will over freeze relatively quickly in autumn, that once that frozen cover is thick enough it would insulate the underlying water, especially if there's a layer of air ( airpockets above water pockets so to say ) that would further insulate the water from the really cold surface due to it's relatively poor conductive capabilities. again i'm sure that those with the background can word this better and/or shed more light, while the existence of embedded lakes i'm 100% positive that they exist because they've been found and in parts explored.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #686 on: July 03, 2016, 08:30:53 PM »
...
Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?

I highly doubt that though I know nothing of the subject. I would assume the melt ponds freeze in winter and melt in summer, and perhaps at some point due to weather they iced over, and now that ice cover melted. Can be checked by looking at LandSat preview images over time in EarthExplorer.

I thought I would agree, but did a spot of internet research.  From Wintertime storage of water in buried supraglacial lakes across the Greenland Ice Sheet, L. S. Koenig, et.al. 2015:
Quote
Abstract.
Increased  surface  melt  over  the  Greenland  Ice
Sheet (GrIS) is now estimated to account for half or more of
the ice sheet’s total mass loss. Here, we show that some melt-
water is stored, over winter, in buried supraglacial lakes. We
use airborne radar from Operation IceBridge between 2009
and  2012  to  detect  buried  supraglacial  lakes,  and  we  find
that they were distributed extensively around the GrIS mar-
gin through that period. Buried supraglacial lakes can persist
through multiple winters and are, on average,
below the surface. Most buried supraglacial lakes exist with
no surface expression of their occurrence in visible imagery.
The  few  buried  supraglacial  lakes  that  do  exhibit  surface
expression  have  a  unique  visible  signature  associated  with
a darker blue color where subsurface water is located. The
volume of retained water in the buried supraglacial lakes is
likely insignificant compared to the total mass loss from the
GrIS, but the water may have important implications locally
for the development of the englacial hydrologic system and
ice temperatures. Buried supraglacial lakes represent a small
but year-round source of meltwater in the GrIS hydrologic
system.

From the introduction:
Quote
This paper presents an initial study and mapping of over-
winter  surface-melt  retention  in  buried  supraglacial  lakes
(Fig.  1)  within  the  GrIS.  We  define  a  “buried  supraglacial
lake”, hereafter for brevity a “buried lake”, as water retained
through a winter season at shallow depths within the ice sheet
that originally formed, during a previous melt season, as a
(subaerial) supraglacial lake.

I learn something every other day!
Arctic ice is healthy for children and other living things because "we cannot negotiate with the melting point of ice"

magnamentis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #687 on: July 03, 2016, 10:24:33 PM »
thanks for providing the many more details and sources :-)

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #688 on: July 03, 2016, 11:35:28 PM »
A one day animation focuses on melt ponds again where the ice cover of many is now breaking up.

Seeing this ice cover melt and break apart, this has to mean that deeper water in these melt ponds never freezes during the winter, right?


I highly doubt that though I know nothing of the subject. I would assume the melt ponds freeze in winter and melt in summer, and perhaps at some point due to weather they iced over, and now that ice cover melted. Can be checked by looking at LandSat preview images over time in EarthExplorer.
depth.  If they are deep enough then they wont freeze to the bottom. How thick does the sea ice get? 3 meters? 6 meters?

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #689 on: July 04, 2016, 12:20:31 AM »
Looks like 2 melt ponds drain, with effects propagating down to the coast.  Perhaps Wipneus will provide a better image?
Edit:  Circled the 2 areas that I see changes downstream.
« Last Edit: July 04, 2016, 12:28:29 AM by solartim27 »
FNORD

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #690 on: July 04, 2016, 01:42:31 AM »
That is a great animation!

It also begs the question and would seem to suggest that melt ponds allow more warm air to pass *through* Greenland, supercooling in the process and being deposited the opposite site of whichever it enters.

That would explain why 2012's catastrophic melt was followed by mild seasons in both 2013 and 2014.

If Greenland acts as an enormous air conditioner for the Northern Hemisphere/Arctic, its "normal" capacity without melt would certainly be substantial. But with a season like 2012 on the books, it would fracture/split in many more locations versus a typical year in the 20th Century (which would have featured very little such activity). And then as you head into fall and solar radiation begins declining, you still have all the nooks and crannies for the air to pour through as it traverses the Greenland Ice Sheet... "activating" it as a much stronger cold source in the process, as the volume of air that can cool through the ice sheet increases dramatically (in addition to heat removed during nighttime/etc).

....of course then it would certainly follow that through the following fall/winter/several seasons, Greenland's cooling power would be enhanced until the nooks & crannies are filled with ice once more.

But perhaps like we've seen in the Arctic, the "new" ice in these locations is much easier to melt vs. the old stuff, which means that the cycle continues repeating & worsening until there is no rebound year and glaciation begins across the NHEM (specifically NE Canada, then spreading from there) once more.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #691 on: July 07, 2016, 01:13:24 PM »
Ice berg breaking, again near Kap Zach.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #692 on: July 07, 2016, 05:20:10 PM »
I think there was something more than an iceberg breaking?  Aqua images.  Yesterday's Polar View sentinel 1 image border goes right down the center of the glacier, I won't be trying to stitch that together. 

Edit:  New cracks appear to be directly downstream from the disappearing melt ponds from Jul 4th gif.
« Last Edit: July 07, 2016, 06:57:06 PM by solartim27 »
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solartim27

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #693 on: July 07, 2016, 09:48:54 PM »
Went back for another look on Terra, glad I did because the clouds on the glacier cleared out.  Looks like the cracks have gone a little further than the earlier Aqua gif.  Here is a gif from 7/2 to 7/7, remarkable how many ponds disappear.  Could some have been snowed over?
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oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #694 on: July 08, 2016, 12:27:42 AM »
Went back for another look on Terra, glad I did because the clouds on the glacier cleared out.  Looks like the cracks have gone a little further than the earlier Aqua gif.  Here is a gif from 7/2 to 7/7, remarkable how many ponds disappear.  Could some have been snowed over?

Looks like some nice calving there.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #695 on: July 08, 2016, 08:33:28 AM »

Looks like some nice calving there.

You can say that. First major calving of this year.

Click on the picture to start the animation.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #696 on: July 08, 2016, 11:34:29 PM »
Looking at this animation, the ice floating in the melt pond upstream from the calving area, moves rapidly upstream in the pond as the calving occurs. Does this suggest the melt pond has actually melted through the glacier and this motion was triggered by waves under the glacier caused by the calving?

magnamentis

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #697 on: July 08, 2016, 11:57:45 PM »
Looking at this animation, the ice floating in the melt pond upstream from the calving area, moves rapidly upstream in the pond as the calving occurs. Does this suggest the melt pond has actually melted through the glacier and this motion was triggered by waves under the glacier caused by the calving?

about the melt through i dunno but if you look for a landmark (not ice) and compare the two images once can see that the entire glacier made a big move downstream and whether or not that is a melt through, it could be that the floes gave in to "Massenträgheit" (inertia?)

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #698 on: July 09, 2016, 06:56:56 AM »
I would guess the motion is wind related, and is one of the same changes I had noticed in the earlier post around the 4th.  I asked Wipneus about the melt ponds vanishing, and he said they were probably not related to the calving.
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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #699 on: July 09, 2016, 12:53:44 PM »
Looking at this animation, the ice floating in the melt pond upstream from the calving area, moves rapidly upstream in the pond as the calving occurs. Does this suggest the melt pond has actually melted through the glacier and this motion was triggered by waves under the glacier caused by the calving?
Could a sudden change in elevation at the face concurrent with the calving event explain what may be a "sloshing" in the melt pond? The katabatic winds wouldn't reverse & this is the only other force that I can think of that would move the ice floating in the melt pond to head back away from the front.
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