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Author Topic: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland  (Read 254433 times)

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #850 on: July 08, 2017, 02:30:48 AM »
the northern end is interesting too, the bergs formed there are narrower than elsewhere along the front where ice which is lee wide than high topples as soon as it separates from the glacier. I assume that means the ice is thinner there. Which would not be surprising with the slower movement it would be exposed to melting from below for longer.
The piece which wipneus focussed on back in March spalled off a southfacing remnant due to sideways pressure. The remnant itself has no forward movement since it is almost separate from the moving glacier.
Sentinel 2A is back as well. Here is a detail of the northern tip of the calving front.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #851 on: July 08, 2017, 09:12:41 AM »
The one-day growth of the smaller melt pond (lower left corner) is impressive!

Interesting that the mélange on the right remains frozen.
This animatiion and others similar to it are what led me to the unconventional conclusion that in ZI the sea ice has a slight buttressing effect (being enclosed by rocks further east), as it forces the glacier to push all the calved bergs, and crush/ridge the sea ice, in order to advance.
This is why I expect more calving activity when the sea ice clears, typically in August, and the delicately balanced front loses support.


Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #853 on: July 12, 2017, 06:48:53 PM »
One of Zachariae's old calvings decides to do something dramatic.

sidd

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #854 on: July 12, 2017, 10:39:16 PM »
Paper on the Cryosphere discuss about 79N, (and Peterman and Ryder). 79N is thinning

"At Nioghalvfjerdsbræ the total melt flux (14.2±1.6 km^3/yr water-equivalent) exceeds the inflow of ice
(10.2±0.59 km^3/yr water-equivalent) indicating present thinning of the ice tongue"

I attach part of fig 1 and fig 2. Nice paper,read the whole thing.

http://www.the-cryosphere-discuss.net/tc-2017-99/


Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #855 on: July 14, 2017, 12:39:36 PM »
A relatively narrow calving is unstable: the calvings topple over.

Tor Bejnar

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #856 on: July 14, 2017, 02:45:04 PM »
Although small, they do a good job at pushing previously calved icebergs away from the front.
Arctic ice is healthy for children and other living things.

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #857 on: July 15, 2017, 10:31:09 AM »
I know this has been done before but I find this so impressive I think it is worth repeating. Images are largely self explanatory I hope, icebergs tip over when they are taller than wide. These bergs are 300m tall!  Quite a splash even with ice that is already afloat (not grounded).
In physics terms the work done to move a lot of bergs a few hundred meters sideways is not easily quantified as energy required (from lowering center of mass of the berg). I expect the upwelling of meltwater below the glacier front will add to the push on the floating bergs towards the sea ice which still covers the bay.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #858 on: July 15, 2017, 07:30:18 PM »
For fun: two melt ponds on the Zachariae Isstrøm, one seems to drain into the other.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #859 on: July 15, 2017, 09:09:46 PM »
For fun: two melt ponds on the Zachariae Isstrøm, one seems to drain into the other.
Thanks, amazing resolution. The draining pond's length is ~1-1.5 km assuming each pixel is 10m. Must have been quite a waterfall.

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #860 on: July 15, 2017, 11:09:27 PM »
reading back through the thread I was reminded of the microcat sensors of itm5 which were placed at 79N last August. What I don't understand is the change in pressure, they all seem to be at lower pressure, 10 dbar less than a year ago. This might be that somehow they are sitting less deep in the water or does anyone have a better explanation? Temperatures have risen at all 4 sensors which isn't explained by a change in depth (if that is what happened) because temperature is higher at greater depth.
http://www.whoi.edu/page.do?pid=154416

Shared Humanity

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #861 on: July 16, 2017, 12:27:20 AM »
For fun: two melt ponds on the Zachariae Isstrøm, one seems to drain into the other.

That is so cool.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #862 on: July 26, 2017, 04:38:07 PM »
Calving to the north of the calving front.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #863 on: July 26, 2017, 04:42:07 PM »
and one more to the south (Kap Zach)

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #864 on: July 26, 2017, 09:31:29 PM »
Interesting that it all moves in concert, suggests to me that it's driven by escaping melt water, not that tide action can altogether be ruled out.

Hyperion

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #865 on: July 27, 2017, 10:41:38 AM »
reading back through the thread I was reminded of the microcat sensors of itm5 which were placed at 79N last August. What I don't understand is the change in pressure, they all seem to be at lower pressure, 10 dbar less than a year ago. This might be that somehow they are sitting less deep in the water or does anyone have a better explanation? Temperatures have risen at all 4 sensors which isn't explained by a change in depth (if that is what happened) because temperature is higher at greater depth.
http://www.whoi.edu/page.do?pid=154416


that is very odd looking. every single one of them looks like its risen more than 10m in the water by the pressure change and all at the same rate. Maybe the cables got all twisted up and tied itself in knots near the surface, giggle. Or someone mistook it for a fishing line and tried to pull it up to see if anything was hooked on it. Or had ideas about recovering some copper for the scrap metal dealer. ;D
Policy: The diversion of NZ aluminum production to build giant space-mirrors to melt the icecaps and destroy the foolish greed-worshiping cities of man. Thereby returning man to the sea, which he should never have left in the first place.
https://en.wikipedia.org/wiki/McGillicuddy_Serious_Party

nukefix

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #866 on: July 27, 2017, 11:05:49 AM »
Interesting that it all moves in concert, suggests to me that it's driven by escaping melt water, not that tide action can altogether be ruled out.
I think that's rather standard with a calving, it looks like the new calved iceberg pushes everything away and ice-melange & sea-ice transfer that impulse quite far.

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #867 on: July 27, 2017, 11:53:07 AM »
Andreas T 'reading back'
 I think Dijmphna sound is a little deeper than the fjord below N79, is it possible bottom melt caused the north end of the 'footprint' to sink raising the ice the sensors are connected to, and redirecting the currents?
« Last Edit: July 27, 2017, 01:30:32 PM by johnm33 »

iwantatr8

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Shared Humanity

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #869 on: July 27, 2017, 03:21:07 PM »
Interesting that it all moves in concert, suggests to me that it's driven by escaping melt water, not that tide action can altogether be ruled out.
I think that's rather standard with a calving, it looks like the new calved iceberg pushes everything away and ice-melange & sea-ice transfer that impulse quite far.

Satellite images of calvings are deceiving. These are high energy, violent events.

solartim27

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #870 on: August 04, 2017, 04:04:54 PM »
Good article here, lots of pictures and video
Approximately 12 percent of Greenland's ice takes this path - and, as scientists have proven in recent years, the velocity of these flows is increasing. "The ice stream seems to be on the brink of a change," says Dorthe Dahl-Jensen of the University of Copenhagen.
Wrapped in a thick blue, down jacket with a fur collar, the silver-haired glaciologist has just stepped off a special plane. She's leading a field camp where scientists are about to research precisely this change. The project is called EastGRIP. In the name of science, a hole will be drilled through Greenland's 2.5-kilometer-thick (1.5 mile) ice shield. To execute the work, around 20 people are currently living right on the ice, at the 75th parallel north.

http://www.spiegel.de/international/world/a-river-of-ice-scientists-study-greenland-s-role-in-sea-level-rises-a-1161220.html
FNORD

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #871 on: August 04, 2017, 08:37:07 PM »
Good article here, lots of pictures and video

Thanks solartim. I found this overview image to be very useful.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #872 on: August 11, 2017, 07:16:44 AM »
The sea ice around Zachariae has started breaking and moving in the last few days, which could lead to a quick flushing of the calved icebergs and ice melange, and possibly some extra calving activity of parts of the front currently hanging by a thread.

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #873 on: August 12, 2017, 11:21:09 AM »
the bergs near the calving front seem to have moved without a calving, but I would want to see a clear Sentinel image to be certain. The sea ice in the bay between the Zachariae glacier and the islands, (Jokelbught I guess?) is mobile but not getting away very far, the exits between the islands are narrow and in the south blocked by remnants of the ice shelf which broke up in 2002 (thats a bit bof a guess, I have not traced them back to that year) image attached
http://apps.sentinel-hub.com/sentinel-playground/?lat=78.09716267271118&lng=-19.786376953125&zoom=9&preset=1_NATURAL_COL0R&layers=B8A,B03,B02&maxcc=99&gain=0.3&gamma=0.7&time=2015-01-01|2017-08-07&cloudCorrection=none&atmFilter=&showDates=false
The largest and clearest exit does not have much transport through it because drift is slow and mostly north along side it it seems from looking at movement in 2016 and 2013.

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #874 on: August 12, 2017, 12:30:45 PM »
looking around on Sentinel I have been intrigued by this meltlake not far from the calving front. As has been commented on elsewhere, these features are located on the glacier surface relative to features of the ground below it. I.e.. as the glacier ice moves along the meltlake stays in a surface depression which probably sits upstream of a bump in the rock surface below the glacier.
I have picked cloud free images from Aug 16 and 17 and the earliest available Mar 17 for an indication of surface contours in low sun angle illumination.
This meltlake does not seem to be very old, I could not see it in the MODIS images before 2014. Therefore it gives an opportunity to follow its development as its effect on the ice moves downstream (of the glacier). Possibly the meltlake has appeared in this location due to thinning of the glacier as the calving front has retreated towards it.
The March image shows a narower part of the lake which seems to have frozen over in the previous winter and I think can be seen again as a darker, deeper area this August. I am looking forward to finding out what happens as this moves towards the rise which stops the lake from draining down towards the sea.
Probably not a profoundly important feature but fun to watch.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #875 on: August 12, 2017, 06:56:02 PM »
Interesting, I guess the lack of melt water makes the pond much smaller to spot in previous years.

Here are a couple of Aster images 2001-2016 stacked together of the same spot.

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #876 on: August 12, 2017, 08:55:12 PM »
Thanks, Wipneus, seeing those previous years shows how much variation there is around this spot. I also find it instructive how little trace these earlier, smaller meltpools have left on the present day glacier. I still think that changes in contours and drainage determines size of the pools and that this year's pool looks deeper to me. Further developments (over a year or two will tell more).

I have looked a bit more at ice berg movements at the exits of Jokelbught. I coloured in some of them at what looks to me like the larges gap in the islands south east of Schnauder oer.  The images of July 2016 and 2017 show that these have not taken the exit despite being very close to it when the sea ice broke up and allowed movement last year. There is mevement, i.e. no signs of grounding, there just seems to be little water movement across that gap, maybe it was different in other years.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #877 on: August 13, 2017, 10:12:40 PM »
I apologize for the terrible resolution, but in my opinion better than nothing, showing the movement of sea ice in the bay, quite limited but after many months of total immobility.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #878 on: August 13, 2017, 11:24:33 PM »
I apologize for the terrible resolution, but in my opinion better than nothing, showing the movement of sea ice in the bay, quite limited but after many months of total immobility.

The flow of debris from Zachariae Isstrøm will probably increase during next 3 - 4 weeks, and 2017 could be one of the rare years when all the fast sea ice at Belgica Bank will leave the area as it did in the beginning of this century and what I believe started the extreme activity at Zachariae Isstrøm during the last 15 years.
Have a ice day!

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #879 on: August 14, 2017, 07:33:57 AM »
A crude Sentinel animation of the bay showing some of the bergs moving away, as well as a minor calving. Interesting that the bergs at the bottom of the image are moving "backwards". The dates are Aug 3rd, 8th and 12th. Click.

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #880 on: August 17, 2017, 10:06:59 AM »
Nice clear day yesterday at N79., shows things opening up for tidal action.
« Last Edit: August 17, 2017, 12:52:36 PM by johnm33 »

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #881 on: August 17, 2017, 10:57:46 AM »
Some recent events: old calvings break, new calving events and developing crack indicating future calvings. Add to that considerable brightening from recent snow fall.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #882 on: August 17, 2017, 11:03:25 AM »
The melt pond discussed by Andreas T has mostly gone.

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #883 on: August 18, 2017, 11:46:46 PM »
I'm wondering how strong the fast ice is, it's certainly looking vulnerable, nothing much changed through the last tidal cycle, except it's 'defences' were swept away. Now with the new moon on monday, and three big tidal cycles up to the equinox things could get very interesting hereabouts.



Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #884 on: August 20, 2017, 06:46:42 PM »
Another thin slice is calving.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #885 on: September 02, 2017, 10:40:16 AM »
So I've been wondering for a while about the old tongue of Zachariae, that got fully separated from the glacier in 2012. I speculate that when it goes, calving activity might pick up due to increased circulation at the front.
It turns out the tongue has been gradually losing bits and pieces, although it's a slow process not expected to finish anytime soon. CLICK to animate Aug 2016 vs. Aug 2017. Note the northeastern corner, the southeastern bulge, and the southernmost bit. For reference, Espen's excellent overview image from up-forum of calving front retreat.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #886 on: September 02, 2017, 09:59:51 PM »
Updated retreatline 2009 - 2017: Click on image to enlarge
« Last Edit: September 02, 2017, 10:14:40 PM by Espen »
Have a ice day!

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #887 on: September 03, 2017, 12:19:09 PM »
Before i saw these pools, center stage, i'd assumed the north side more or less followed the gradient of the glacier slope, does anyone know if they're tidal?

Looking south there are 5  pieces of the old tongue which eyeballing their debris seem about 200+m thick and look like they're going nowhere, but plenty of the debris looks vulnerable to still warm Atlantic waters and the vagaries of wind and tides, and if it melts or moves away could leave a lot of space for Zachariae to fill.
 

nukefix

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #888 on: September 12, 2017, 05:37:40 PM »
I think there has been meltwater exiting Zach that has been melting sea-ice close to the calving front. The feature 1st appears on the 26.8. S-2 image:

http://apps.sentinel-hub.com/sentinel-playground/?lat=78.98372644988251&lng=-20.759353637695312&zoom=11&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=100&gain=0.3&gamma=1.0&time=2015-01-01|2017-08-26&cloudCorrection=none&atmFilter=ATMCOR&showDates=true&evalscript=

johnm33

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #889 on: September 12, 2017, 06:46:53 PM »
I was thinking it was displacing the bergs seawards, surprised there's not more calving. Better link

Andreas T

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #890 on: September 12, 2017, 09:58:22 PM »
The melt pond discussed by Andreas T has mostly gone.
on the 1. Sept it looked completely gone, drained and frozen till the next season I thought but on the 10. there is more water which seems to have floated the ice cover on the southern lake.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #891 on: September 17, 2017, 08:06:50 PM »
It looks partly drained, and frozen over again (as most other melt ponds are now).