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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 575402 times)

Adam Ash

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #900 on: August 20, 2015, 03:34:44 PM »
Further to my ramblings about alternate sliding possibilities... (Don't fret I will drop it soon!)

While (as I understand it) the generic ice flow model looks at plastic flow of the entire depth of the glacier, I see a couple of bits of evidence from recent posts which leads me to wonder about the full-depth plastic flow model.

1.  Having re-watched that Chasing Ice video, I see that many of the icebergs which ended up floating at the calving face had dimensions of tens to (it seemed) hundred of metres above water level, and many of the bits which ended up lying on their sides were potentially of the 1000 metre class.  Some of the bits which calved clearly had a huge underwater draft.  So a lot of that calving event seemed to be from an ice face with a full 1000 metre draft.   

But when I look at the images in current posts of this recent calving the melange does not seem to contain those big pieces.  This could suggest that the calving was from a tongue of just moderate draft (200 to 500 metres perhaps).

This thinner slab could result from either a top-slab sliding out into the calving area and breaking off, or a rapid undercutting of a full face by warmer water, or a combination of all three (there is always an alternative explanation).

2. Second bit of 'evidence' is the nice base profile in post #882. This shows a significant high point about 10 km up from the calving face.  The ice thickness here reduces to about 60% of the depth either side of it.  There is a corresponding reduction in the thickness of the ice there, but only a very slight increase in ice surface level immediately downstream.

If the plastic flow model is true, then (assuming a similar channel width through and either side of this high point) the velocity of the ice over this shallow section must increase (by ~150%?) in order to sustain the mass-flow rate past the point.

Looking at the available imagery I do not see any 'concertina-ing' of the ice mass as it passes that point, or any other evidence that the velocity over the shallows is somehow ~150% of the velocity either side of it.  With a peak observed velocity of around 50 metres per day (about 3.4 furlongs per fortnight, for the more scientifically-minded among us) I doubt that V^2/2g surface level suppression of the flow makes much difference to the surface level or cross section in this case.  So somehow a constant mass-flow (which for almost-solid relatively incompressible ice would mean: for constant volume per unit time past a point) is occurring along the glacier channel in spite of the cross section varying considerably and the surface velocity (seemingly) remaining largely unchanged over the choke point.

A way to resolve this difficulty could be to adopt my suggestion - that the glacier ice (at times) moves as a comparatively shallow sheet which maintain fairly uniform depth (hence cross section) - with the base of the moving sheet clipping the tops of the 'high spots' of the basement of the channel.

I acknowledge that I have not seen any evidence of slab-flow above water level at the calving face in any of the many videos I have seen of calving glaciers, but I do see many layers of clearer ice lenses and horizontal mid-depth tunnels where clearly there are / have been bodies of free flowing water at various depths in the glacier.

To support data acquisition from satellite  imagery, sending a helicopter over the glacier with a fire bucket full of red paint (or sea water+ a kg bag of Rhodamine-B) and regularly dumping big red spots along  selected cross sections would facilitate easier calculation of surface velocity, and any leaks of R-B at the calving face would give info on in-glacier hydraulics.  (Besides, there would be a certain macabre pathos to be found in the sight of a glacier bleeding as it dies!)

Just a thought...

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #901 on: August 20, 2015, 09:09:42 PM »
rapid undercutting of a full face by warmer water
That's surely what's trending today in West Greenland glaciology: seasonally peak meltwater gushing out at respectable velocity at the bottom of the calving face, rising to the surface because as fresh water it is less dense (more buoyant) than fjord saltwater, entraining a flow of replacement ocean water that caverns out the face around the meltwater exits.

The coupling of up-glacier moulin meltwater to ocean circulation comes about from turbulent mixing at the face. Without this effect, stagnant ocean water at the face would melt ice quite slowly and not undermine the upper face.

Notice that the true color NASA imagery shows only a hint of till turbidity in immediate melange on day 228 whereas in the very NE corner of the image turbidity is quite pronounced (showing it is displayed when present). At this point in time, we couldn't even begin to plot the volume and sites of meltwater exit over the season.

Even as we await actual observational sonar imaging (AGU 2015 abstracts) of the bottom of the calving face, not to mention a factually revised elbow DEM from air gravity inversion, it's good to read and re-read the abstract describing what is at the bottom of this glacier: it's not in contact with bedrock but rather gliding on 100 m of sediment and till layers. What fraction of that is hydrated (and what fraction of that water is liquid at what temperature) remains unknown, as is the erosional effect of moulin meltwater drainage.

The abstract by G Tsoflias (post #881) uses a seismic track to image sub-glacial sediments along the southern branch, concluding that the sediments between 35 and 200 meters thick overlie bedrock as three distinct facies: a basal till layer, accreted sediments and re-worked till. The basal till and accreted sediments vary in thickness from less than 5 m to nearly 100 m thick, with liquid water occupying 200 m along a trough at the ice-sediment interface.
« Last Edit: August 20, 2015, 09:22:04 PM by A-Team »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #902 on: August 20, 2015, 09:38:46 PM »
I asked Joshua Steven, the senior imagery specialist at NASA Earth Observatory if he could disclose some of their image processing tricks, notably how the two Landsats were processed so nicely to natural color. He got back to me right away with a very helpful response.

Much to my surprise, this did not involve pages of command line in expensive proprietary software we had no prospects of ever duplicating, nor did it involve rational scientific algorithms based on deep physical principles from electromagnetic theory. Instead, he just uses Photoshop on an iMac. In other words, each image is different and color correction remains a bit of an art form to get them looking attractive without loss of scientific attributes.

He starts with bands 432 for RGB, then:

use curve adjustments to brighten the image and bring their color more inline with what a high-altitude observer would see. Landsat scenes often come out looking a bit blue due to Rayleigh scattering and atmospheric haze. So toning down the blues does a great deal in making the overall color more realistic."

The method we use at the Earth Observatory is described in an excellent tutorial written by my predecessor, Rob Simmon. It can be found here: http://earthobservatory.nasa.gov/blogs/elegantfigures/2013/10/22/how-to-make-a-true-color-landsat-8-image/

Tom Patterson at the National Parks Service has written a similar tutorial, that also includes pansharpening: http://www.shadedrelief.com/landsat8/introduction.html

Other readers have asked about doing the color correction in ArcGIS, so I am currently working on a tutorial for that. It should be posted in the next couple of days.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #903 on: August 20, 2015, 10:11:56 PM »
More action at Jakobshavn (Sorry I dont have any Sentinel data from Aug. 16 2015)
Have a ice day!

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #904 on: August 20, 2015, 10:52:29 PM »
Right, Sentinel has not been by this way since the 13th. Not likely they will goose the orbit just because some internet forum wants more coverage of a particular glacier.

Hopefully nukefix can work some magic on the Landsat-compatible georeferencing of the 13th and 20th. (It's explained well over at Developers Corner but I've not had time to dig into that yet.)

I will lighten up the animation and rotate it a bit shortly

wili

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #905 on: August 20, 2015, 11:17:36 PM »
How much further back is that thing likely to go this melt season?
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #906 on: August 20, 2015, 11:55:23 PM »
How much further back is that thing likely to go this melt season?
The animation below aligns the 20 Aug 15 Sentinel of Espen's post above with the 16 Aug 15 Landsat day 228. There was a rotation of 21.8, a rescaling of 80%, and translations of ground control points, all done more accurately had nukefx's protocol been used. I dropped the 13th because it confused the comparison. Basically there seems to be little change since the post-event Landsat.

Since the glacier front has advanced 35 m each day, this means calving has kept up but not gained ground. The calving front retreats only when calving exceeds advance.

Last two years, the maximal retreat seems to have been in late September, so five weeks to go other things being equal (which they never are).

There are five distinct issues here:

-- what caused the record event, anything special going on?

-- what will happen next, is this the beginning of a new regime?

-- where will the calving front end up, how does relief of buttressing affect main and marginal inflow?

-- what is going on with ice stream velocity, acceleration relative to previous years, and volume discharge (SLR)?

-- what will happen over the winter in terms of net advance of the calving front?

It's great to see four leading scientists with extensive experience with Jakobshavn commenting in the Nasa feature. Will they make predictions? (My prediction is no, none of them will get into specifics.)
« Last Edit: August 21, 2015, 12:14:28 AM by A-Team »

wili

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #907 on: August 21, 2015, 05:25:48 AM »
Thanks for a more detailed answer (with supplemental questions!) than my simple-minded question deserved.

I am in no position to do so myself, but it does seem to me that it would be a valuable, if perhaps humbling, learning experience for those who know most about the ice up there and its dynamics to try to come up with hypotheses about what exactly will happen next and why. Then we could see how things actually panned out and figure out where the assumptions were wrong.

Kind of the closest thing we get to testable hypotheses in real world large scales situations like this. Of course, they're not exactly repeatable, but unfortunately we are bound to see more sea-bound glaciers passing these tipping points in the future to apply knowledge from this one to. I suppose it's all academic, but that's what academics (and various and sundry ice nerds) do, isn't it?
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #908 on: August 21, 2015, 11:46:25 AM »
S-1 views the carnage 19.8.2015 (IW in UTM Zone 22 15m pixel size).

edit: S-1 product filename is erroneous in the jpg, the image has been processed from product S1A_IW_GRDH_1SSH_20150819T204653_20150819T204718_007337_00A135_2D70
« Last Edit: August 21, 2015, 11:51:28 AM by nukefix »

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #909 on: August 21, 2015, 12:16:43 PM »
The animation below aligns the 20 Aug 15 Sentinel of Espen's post above with the 16 Aug 15 Landsat day 228.
Try with the S-1 IW I just posted above..should look great (I hope)!

oren

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #910 on: August 21, 2015, 01:55:30 PM »
I wonder if anyone is counting the total JH flux. It's might be still negligible, but now JH is not only width x depth x annual velocity of main branch + retreat, instead there's all sorts of ice crumbling into the much-longer fjord from newly-exposed cliff faces especially from the north side. The hi-res animations show it quite well.

Wipneus

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #911 on: August 21, 2015, 04:32:18 PM »
Also ESA has released an image about the Jakobshavn calving:

Chasing Ice


A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #912 on: August 21, 2015, 04:48:52 PM »
anyone measuring total JH flux....all sorts of ice crumbling into the much-longer fjord from newly-exposed cliff
Briefly, I am headed out on a camping trip and will be offline for a few weeks.

Probably not. The velocity is so much greater in the main south channel that it dominates the discharge volume. However it would be picked up in total mass balance loss of Greenland as measured by GRACE (though it would slip through the cracks of overall measurement error).

The animation below shows the post-calving NASA Landsat aligned with nukefix's mercatorized Sentinel at the divider between north and south branches. They are off by a rotation of 5.53º by the lake, the other useful ground control point. Not clear where this discrepancy arises but I will try again to see if ESA got the same re-projection.

The second animation shows a region of ambiguous calving whose interpretation affects overall interpretation of area calved by the time of the 16 Aug 2015 Landsat. Note it is reproduced quite well in the Sentinel images of the 19th and 20th. It looks to me like the area with the yellowish tint has slumped into the fjord but is still 'leaning' against the main calving front (or pinned on a rock wall protrusion). The reddish area shows one of the component sub-streams seemingly pushing into this area.
« Last Edit: August 21, 2015, 05:00:56 PM by A-Team »

AbruptSLR

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #913 on: August 21, 2015, 05:04:30 PM »

There are five distinct issues here:

-- what caused the record event, anything special going on?

-- what will happen next, is this the beginning of a new regime?

-- where will the calving front end up, how does relief of buttressing affect main and marginal inflow?

-- what is going on with ice stream velocity, acceleration relative to previous years, and volume discharge (SLR)?

-- what will happen over the winter in terms of net advance of the calving front?

To re-state (from other threads) the obvious:
(a) The linked reference indicates that GFDL CM2.1 finds that the AMOC is changing to increase warming of the subpolar gyre (SPG, see the attached image), while cooling the adjoining Gulf Stream region, as projected by Hansen et al 2015.  Warming the SPG allows the Irminger Current to carry warmer water to Disko Bay:

Zhang, J, and Rong Zhang, July 2015: On the Evolution of Atlantic Meridional Overturning Circulation (AMOC) Fingerprint and Implications for Decadal Predictability in the North Atlantic. Geophysical Research Letters, 42(13), DOI:10.1002/2015GL064596.

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064596/abstract

Abstract: "It has been suggested previously that the Atlantic Meridional Overturning Circulation (AMOC) anomaly associated with changes in the North Atlantic Deep Water formation propagates southward with an advection speed north of 34°N. In this study, using Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 (GFDL CM2.1), we show that this slow southward propagation of the AMOC anomaly is crucial for the evolution and the enhanced decadal predictability of the AMOC fingerprint—the leading mode of upper ocean heat content (UOHC) in the extratropical North Atlantic. A positive AMOC anomaly in northern high latitudes leads to a convergence/divergence of the Atlantic meridional heat transport (MHT) anomaly in the subpolar/Gulf Stream region, thus warming in the subpolar gyre (SPG) and cooling in the Gulf Stream region after several years. Recent decadal prediction studies successfully predicted the observed warm shift in the SPG in the mid-1990s. Our results here provide the physical mechanism for the enhanced decadal prediction skills in the SPG UOHC."

(b) Due to the high flow rate of Jakobshavn, the surface elevation near the calving front keeps decreasing (due to ice thinning); which destabilizes the ice-face as buoyance forces exceed gravitational forces (on the chunk of ice downstream of the last crevasse parallel to the calving front).

(c) The crevasse pattern in the ice can facilitate early calving (as we saw for the Pine Island Ice Shelf this July), and looking at the fracture pattern upstream of the middle of the Jakobshavn calving face, I believe that this ice can calve more readily than that on the adjoining ice face. 

(d) Obviously, if the calving front has moved upstream of any local sill or side-wall buttressing, then this could move Jakobshavn into a new calving regime.

(e) Fluctuation in the buttressing from the mélange are of fundamental importance and can be influenced by the flushing action of the floating ice out of the fjord.

With several weeks to go in the summer season, it will be quite the show to watch.
« Last Edit: August 21, 2015, 06:52:51 PM by AbruptSLR »
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A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #914 on: August 21, 2015, 05:15:18 PM »
The account at ESA, written by an unknown person following this issue in some detail, needs to be read closely for its area (12.5 km2) and volume measurements (17.5 km3 assuming 1400 m depth) because the Sentinel bracketing dates (27 July, 13  19 August) are wider than our Landsats.

http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Chasing_ice

"The new face of the glacier has been pushed inland by several kilometres to what appears to be its furthest easterly location since monitoring began in the mid-1880s. The volume calved could cover the whole of Manhattan Island by a layer of ice about 300 m thick. [[Yes but how deep would it cover the ESA headquarters in Paris?]]

Jakobshavn glacier drains 6.5% of the Greenland ice sheet, producing around 10% its icebergs. This amounts to some 35 billion tonnes of ice that calve every year.

Other similar events have been documented where the glacier parted with 7 sq km of ice, both earlier this year and back in 2010." [[In other words, a record calving relative to contemporary ramp and sill position]]

The high resolution image 7756 x 5003 143 MB is geocoded and possibly re-projected to Landsat mercator; it is located at :
http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2015/08/chasing_glacier_retreat/15562607-1-eng-GB/Chasing_glacier_retreat.jpg

The image uses Sentinel-1A images from 27 July, and 13 and 19 August as the red, green and blue channels, showing the position of the calving front and "other dynamic features" on each respective date. In second image, I split the ESA RGB into its channels, fixed contrast a bit and animated. It is still a stretch to see the westernmost extension of the calving front (they placed a huge white arrow to close to the data) and I would say we have it better characterized here.

The angle between the ground control points is identical to that provided by nukefix, again it does not match that of Nasa's Landsat. This raises the question whether something is wrong in SNAP toolbox procedures as 5.53º is way too far off.

One thing's for sure: this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.
« Last Edit: August 21, 2015, 06:16:09 PM by A-Team »

Iceismylife

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #915 on: August 21, 2015, 06:02:24 PM »

The coupling of up-glacier moulin meltwater to ocean circulation comes about from turbulent mixing at the face. Without this effect, stagnant ocean water at the face would melt ice quite slowly and not undermine the upper face.

I read a paper that quoted 10 meters per year for ice lose per degree above melting.  That works out to 2.7 cm per day.  I think the assumption was un-pumped by a current.  With the current surface sea temps of around 45~50 deg F. That gets you about five inches of fresh water added to the fjord for every square inch of wetted ice area a day.

The fresh water emanating from under the glacier entraining more sea water would be on top of that.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #916 on: August 21, 2015, 06:10:15 PM »
One thing's for sure: this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.


Hello A-Team! that is what they are getting paid for? And that is what the whole circus is all about, but "the amateurs" are normally quicker though!
Have a ice day!

Iceismylife

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #917 on: August 21, 2015, 06:47:28 PM »
...

One thing's for sure: this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.
That is the quote of the year.

OK my $0.25 worth.

It looks like we've had two large pieces come off at 2/3 of a km thickness in resent calvings.  So take that as the ice thickness.  This would have been a free floating tong of ice.  That was cantilevered over the sill and grounding line.  Someone has observed that there have been surges in the fjord. One happened just prior to the big calving event.  The first depression prior to the sill would be a logical reservoir to fill and drain to cause the surges.  So a surge just before the new moon would load the top of the glacier after the sill in tension.  The high tide with the new moon or the low tide with it would have put higher stresses into the system.  And we are now on the other side of the sill.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #918 on: August 21, 2015, 08:28:57 PM »
Neven our questions are responded somehow:

"Recently we learned that the Jakobshavn Glacier, one of Greenland’s fastest sliding, may  have just lost the biggest piece of ice that scientists have yet seen — on the order of 5 square miles in area on its surface. "Perhaps the most troubling thing is that scientists don’t even know if that’s a record: Greenland is incompletely monitored, so they can’t really say for sure."

To add my humble opinion ( not a so called expert) I am pretty sure this calving session (to be more precise) is the largest since the tabular age of Jakobshavn (period)!!!!!!!


http://www.washingtonpost.com/news/energy-environment/wp/2015/08/20/greenlands-stunning-melting-in-24-unforgettable-images/
« Last Edit: August 21, 2015, 09:16:08 PM by Espen »
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #919 on: August 21, 2015, 10:57:27 PM »
-- this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.
-- that is what they are getting paid for? And that is what the whole circus is all about, but we're normally quicker!
They need to get their facts straight or go home. I propose docking their next paycheck for "48 hours" and putting it in the tip jar. Let's start with my post #805 of August 14 (420 views):

"There is quite a bit of calving ahead. Again I am not recalling this level of frontal disintegration so far upglacier. The scale here is 7.5 m per pixel [[image from Landsat B8 band]], meaning that everything 4 pixels in from the calving front will be gone tomorrow."
Do the math. 'Tomorrow' in the context of an August 14th post means August 15th. If I had intended August 16th, well the "day after tomorrow' was available for that. What part of g.o.n.e don't you understand?

Sure enough, Espen catches the 14/15th overnight event on a Modis pair so helpfully provided by DMI, puts up co-registered animations twice (posts #808 and #809, 362 views) at 10:35:17 PM and 11:01 PM followed by confirmation ruling out cloud artifacts via advanced image enhancement and a third 14-on-15 reverse animation 11:21 in my post #808, 353 views. We're still around noon on August 15 and this event has largely been consummated within a 24 hour time frame as predicted the day before.

Remember the scientific community's shabby treatment of Patrick Lockerby and the calving of Petermann (with the important exception of Andreas Muenchow)? I do. And Lockerby did it with physics, not just looking at satellite photos.

Espen you can run from the term 'scientist' but you cannot hide from 'Expert Observer' status, having looked at maybe 5x the number of satellite images of Greenland as the nearest scientist. And I'll go mano-a-mano with any of these clowns for who's who overall in science. Sure I explain stuff here but I can make it incomprehensibly complex (is there an audience for that?).

Meanwhile, the ESA has misinformed 2,083 visitors so far to which we could add more millions of WaPo and general internet readers. We try to arrive at the facts here and get the word out -- but so far that's only been to 420 visitors (going by count maximum under images).

So a new twist on an old saying: the bullsh*t got half way around the world even though the truth did already have its pants on. And six months from now, you'll see a journal article re-creating (plagiarizing) the animations and analysis above (Not-Invented-Here-By-One-Of-Us).

Too bad the gear's all gone, nobody monitoring anything that we know of:

Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland
JM Amundson, M Truffer, MP Lüthi, M Fahnestock, M West, and RJ Motyka
http://onlinelibrary.wiley.com/doi/10.1029/2008GL035281/full

During summer 2007 we deployed several instruments, all synchronized to UTC time, to study Jakobshavn Isbræ and its proglacial fjord before, during, and after large calving events. Three cameras took photos of the terminus and fjord every 10 minutes from 13 May to 8 June 2007, every hour from 8 June to 17 August 2007, every six hours from 23 August 2007 to 7 May 2008, and every 10 minutes from 7 May to 14 May 2008.

Ocean and seismic waves from calving events were recorded with a tide gauge and a seismometer. A Keller DC-22 pressure sensor, which has a resolution of 0.002 m, was placed in Ilulissat Harbor, 50 km west of the glacier terminus; it logged data every 10 minutes from 11 May to 22 August 2007.

A Mark Products L22 3-component velocity seismometer was placed on bedrock 1 km south of the glacier terminus and ran with a sampling frequency of 200 Hz from 17 May to 17 August 2007 and 100 Hz from 22 August to 22 November 2007 and from 9 April to 9 May 2008. The data gap in winter was due to a loss of battery power. The instrument has a natural frequency of 2 Hz and a sensitivity of 88 V s m−1.

Optical and GPS surveys were conducted to monitor iceberg and glacier motion. Six survey reflectors were placed on the lower 4 km of the glacier and surveyed every 15 minutes with a Leica automatic theodolite from 15 May to 9 June 2007. Nine dual-frequency GPS receivers were deployed higher on the glacier, five on the main flow line and four on a perpendicular transect. These units were installed between 22 May and 1 June 2007 and, except for three that failed in July, ran until 23 August 2007.

Additionally, two telemetered GPS units were placed on large icebergs; data from these were retrieved from 29 May to 8 June 2007. All GPS units logged position data every 15 seconds. The data were differentially corrected against one of two base stations located on opposite sides of the fjord. The measurement uncertainties of the optical and GPS surveys were estimated by de-trending several days of data at a time, removing extreme outliers that clearly indicate bad surveys, and calculating the root mean square errors. The errors for the optical and GPS surveys were ±0.15 m and ±0.02 m, respectively.
« Last Edit: August 22, 2015, 12:04:23 AM by A-Team »

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #920 on: August 21, 2015, 11:55:13 PM »
Hello WaPo ... just looking at the 24 old photos in your 20 August 15 listicle on Jakobshavn's recent record event.

Did you know that all the images and animations on these forums are FREE FOR THE TAKING? Yes that's right, brand new, not previously published, open source, public domain, no IP rights retained, no copyright, no watermarks, no permissions, no secondary infringements, no credits (site link appreciated), nothing to do, good to go.

Yes it's true -- when we upload our work to the open internet here, we do so knowing it's in the wild, beyond recall, out of our control, gone, anybody can use it however they want and guess what we don't lose any sleep over it.

Tabular iceberg in Uummannaaq in 2010 -- are you sure that's where and when this photo was taken?
« Last Edit: August 22, 2015, 12:08:53 AM by A-Team »

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #921 on: August 22, 2015, 08:59:13 AM »

The angle between the ground control points is identical to that provided by nukefix, again it does not match that of Nasa's Landsat. This raises the question whether something is wrong in SNAP toolbox procedures as 5.53º is way too far off.
According to this it's the Landsat that is "off" since it's not in UTM but in Polar Stereographic at the latitude of Jakobshavn.

http://landsat.usgs.gov/landsat8.php

skanky

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Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #923 on: August 23, 2015, 10:09:46 PM »
Jakobshavn gained a little since the big calving event last week:

« Last Edit: August 23, 2015, 10:23:27 PM by Espen »
Have a ice day!

solartim27

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #924 on: August 23, 2015, 11:58:54 PM »
Had a nice clear Terra image today, with no sign of a surge into the bay after the big collapse.  I can't imagine that it happened and dissipated during the cloudy days.  Could there have been a big meltwater drainage before the collapse that undermined the front, causing the collapse?  And how many licks does it take to get to the center of a tootsie roll lollipop?
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nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #925 on: September 01, 2015, 11:32:08 AM »
S-1 IW 31.8.2015 in UTM22 15m pixel size. No new big calvings.

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #926 on: September 01, 2015, 12:12:02 PM »
Animation between S-1 IW 19.8.2015 & 31.8.2015. Click to animate.

georged

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #927 on: September 02, 2015, 12:05:07 AM »
Can Jakobshavn credibly be called one glacier anymore? The northern front and and the eastern front appear to be operating quite independently.

The designation as a single glacier with two feeds made sense until about 2005-2006, but a decade later there is absolutely no sign that the two fronts will ever unify again.

Seumas

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #928 on: September 02, 2015, 12:38:43 AM »
That's a good question. Is it like ice shelves, where we'll end up with Jakobshavn-A and Jakobshavn-B ? Or maybe Jakobshavn North and Jakobshavn East.

Is there a set naming scheme for when this happens?

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #929 on: September 02, 2015, 07:23:44 AM »
I believe that at this point there is just one glacier or ice stream - the south branch. The north branch and the new north-wall-of-the-south-branch are areas where the ice sheet is calving or flowing directly into the sea. More like "ice falls".

plinius

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #930 on: September 02, 2015, 05:01:30 PM »
I am not sure I understood your distinction. Isn't the main branch also just calving directly?

AbruptSLR

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #931 on: September 02, 2015, 05:50:20 PM »
I believe that at this point there is just one glacier or ice stream - the south branch. The north branch and the new north-wall-of-the-south-branch are areas where the ice sheet is calving or flowing directly into the sea. More like "ice falls".

Per the linked Wikipedia article, an icefall is a much different thing than what is occurring at the north branch:

https://en.wikipedia.org/wiki/Icefall

Extract: "An icefall is a portion of some glaciers characterized by rapid flow and a chaotic crevassed surface. Perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/or narrows. The term icefall is formed by analogy with the word waterfall, a similar, but much higher speed, flow phenomenon.

Most glacier ice flows at speeds of a few hundred metres per year or less. However, the flow of ice in an icefall may be measured in kilometres per year. Such rapid flow cannot be accommodated by plastic deformation of the ice."
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Lennart van der Linde

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #932 on: September 02, 2015, 09:41:39 PM »
Some nice airial footage of Jakobshavn calving in May 2014:
http://jasonbox.net/what-massive-greenland-iceberg-calving-looks-like-from-the-air/

oren

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #933 on: September 03, 2015, 07:30:23 AM »
I apologize for the use of layman terms. I mean that when looking at satellite images, you can easily see the main ice stream of the south branch coming from the interior. Visually I see a big difference between that and whatever the north branch should be called.

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #934 on: September 03, 2015, 07:48:43 PM »
From Washington Post:

"According to Box, the iceberg calving observed last month might have been one of the largest breaks for this glacier — though it wasn’t the largest. That distinction might go to a break that occurred between 2002 and 2004 and was about 1.5 times the size of Manhattan."

So now we are talking about a record calving lasting 2 years from 2002 to 2004, that is a new standard!?

And by the way in 2002 - 2004 the glacier calved tabular calves.
That is a completely different ball game!

http://www.washingtonpost.com/news/energy-environment/wp/2015/09/02/watch-as-a-massive-chunk-of-ice-breaks-off-of-the-worlds-fastest-melting-glacier/
« Last Edit: September 03, 2015, 08:25:47 PM by Espen »
Have a ice day!

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #935 on: September 04, 2015, 02:21:38 AM »
Yes, this is a new ballgame. we are at the 1Km cliff instability there even without surface melt and crevassing. In this context, I have been reading the appendices and supplementaries to the Pollard(2015)  open access paper http://dx.doi.org/10.1016/j.epsl.2014.12.035 and what i find is not encouraging. I will try to post some thoughts somewhere.

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #936 on: September 12, 2015, 04:55:07 AM »
A few days ago, temps were very high along the edge of the ice sheet near Jakobshavn, and it may even have rained.  Unfortunately, clouds have obscured the region ever since, so there are no good views, but it still seems to me that something has been going on there, and this satellite photo has a very odd spot that looks like water:

http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2015253155500-2015253160000.250m.jpg

solartim27

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #937 on: September 12, 2015, 07:17:02 AM »
The calving front is cut off, but something (wind?) pushes this berg a good ways down the channel.  Starts right past the blue edge on Sept 6th,  second shot from the 11th.
« Last Edit: September 12, 2015, 07:35:58 AM by solartim27 »
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solartim27

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #938 on: September 12, 2015, 07:23:15 AM »
Here's a wider look for Sept 1, 6, and 11 from DMI
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TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #939 on: September 12, 2015, 07:21:57 PM »
I may be confused by effects caused by clouds, but I am "speculating" that things are going on with the edge of the ice sheet near Jakobshavn and also perhaps there may have been further ice falls.  I have to wonder what this is (see image) -- it's to the south of Jakobshavn (from the link posted above). Also, there are still some very large supraglacial lakes that seem to be unusual for this time of year:


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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #940 on: September 12, 2015, 09:43:54 PM »
I may be confused by effects caused by clouds, but I am "speculating" that things are going on with the edge of the ice sheet near Jakobshavn and also perhaps there may have been further ice falls.  I have to wonder what this is (see image) -- it's to the south of Jakobshavn (from the link posted above). Also, there are still some very large supraglacial lakes that seem to be unusual for this time of year:

Is the location where indicated in red circle or somewhere else?

featurelocation by crandles57, on Flickr

Does seem a little odd. 367 and 721 bands also seem to indicate water rather than clouds or ice or land. Snow won't create a dam and it would be pretty unlikely for hail/ice pellets to freeze together sufficiently to be able to create any significant dam.

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #941 on: September 13, 2015, 07:22:40 AM »
That's a very good comparison photo -- thanks!

I have been watching -- for years -- what looks like "steam" clouds near the sites of supraglacial lakes when they drain.  But this time it does appear that this hole is over land or near the sea, not ice.

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #942 on: September 13, 2015, 07:26:05 AM »
There is another phenomenon that relates to that side of the ice sheet.  Generally, several supraglacial lakes appear to drain at nearly the same time (or over a day or two).  I have to wonder if there is a connection.  But what could that connection be?   It was only recently discovered that there were vast amounts of water under the surface of the ice sheet.  Could it be that this water drains in places, which might then cause the lakes on the surface above to also drain?

solartim27

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #943 on: September 13, 2015, 08:27:40 AM »
There is a possible view of a lake draining from up in the northeast on this message from
L. Bistrup Bræ / Storstrømmen / Dove Bugt / North East Greenland

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TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #944 on: September 13, 2015, 08:58:15 AM »
That's a good example of water continuing to flow out from under the calving fronts. 

In 2010, that sort of thing continued well into December.  I imagine it will again this year.

solartim27

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #945 on: September 13, 2015, 10:02:13 PM »
Here is a gif between Sep 6 and 12.  I don't see any major changes in the calving front, but note the difference in motion of the bergs labeled A, B, and C.  I believe berg A does not move, but appears to because of the different resolutions, sattelite position, and my matching errors.
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nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #946 on: September 14, 2015, 12:00:19 PM »
S-1 IW 19.8.2015/31.8.2015/12.9.2015. Processed with ESA SNAP and Easy GIF Animator. Click to animate.
« Last Edit: September 14, 2015, 12:18:43 PM by nukefix »

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #947 on: September 14, 2015, 12:44:40 PM »
Some observation based on the animation above:

- freezing of the ice melange seems to be setting in in the last frame
- northern side of the southern branch seems to be flowing faster than the southern side
- there a new "calving" in the northern wall of the south branch in the last frame

AbruptSLR

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #948 on: September 14, 2015, 10:46:36 PM »
The linked article provides a nice summary of both observed and modeled ice mass loss from Jakobshavn from 1990 through 2014 (see attached plot):

Muresan, I. S., Khan, S. A., Aschwanden, A., Khroulev, C., Van Dam, T., Bamber, J., van den Broeke, M. R., Wouters, B., Kuipers Munneke, P., and Kjær, K. H.: Glacier dynamics over the last quarter of a century at Jakobshavn Isbræ, The Cryosphere Discuss., 9, 4865-4892, doi:10.5194/tcd-9-4865-2015, 2015

http://www.the-cryosphere-discuss.net/9/4865/2015/tcd-9-4865-2015.html
http://www.the-cryosphere-discuss.net/9/4865/2015/tcd-9-4865-2015.pdf


Abstract: "Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990–2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (GrIS), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the GrIS mass loss and the future sea level rise may be larger than predicted by existing modelling results."
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sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #949 on: September 17, 2015, 05:20:31 AM »
At the same journal, there is an earlier paper bu Hughes and some of the usual suspects comparing Byrd and Jacobshawn in the context of flow under ice-bed uncoupling, using a nice geometical approach outlined by Hughes in earlier papers

http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.html