Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland

[oren]

Thank you A team for the lovely reference on ice thickness etc.

Looking at ice thickness up Jakoshavn and assuming an average retreat of 1.5 km or 1 mile a year for the next 50 years, it looks like Jakobshavn could raise sea level world wide by 150 to 300 mm.  (6 inches to 1 foot)  That would be by 2065.

What does the IPCC say the sea level rise for the world should be by then?

I believe the main contribution of JH to sea level was through its speed (and acceleration), not through its retreat. 15 km/year and more beats 1.5 km/year.

[Espen]

Yes thinning is the real issue to most glaciers in Greenland, not retreat that much!
But that said, retreat is a better explaining tool

[Espen]

Here is a gaining report:

It is amazing how much the north eastern part of the southern branch can grow in such a short period?

But there is show retreat seen at the northern branch (western part).

[A-Team]

Yes, it seems like a lot of things changing this year. For example that brownish basal till in the August image -- we've seen that streaking in the north branch last year but I am not recalling for the channel. Seems like it should be associated with the giant berg but that connection is not evident to me.

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, meaning that everything 4 pixels in from the calving front will be gone tomorrow. The yellow boxes are 28x28 pixels or a week worth of glacial advance @ 30 m/day.

The second image shows the extent of ablation. The loss of snow cover over a wide region is exposing the crevasse field for a long ways in the ice stream drainage basin. It seems like nunataks are showing along the channel walls like never before for this date. Have to click to see at 15 m resolution.

[Shared Humanity]

Here is a gaining report:

It is amazing how much the north eastern part of the southern branch can grow in such a short period?

But there is show retreat seen at the northern branch (western part).

Every time you provide a close up animation, I look at what is going on at the northeastern wall of the southern branch. Retreat of the main calving face has unlocked a lot of ice. I think this will be repeated as the calving face continues to retreat. Meanwhile, this newly freed ice which is grounded below sea level is going to continue to dump a lot of ice.

[Iceismylife]

Thank you A team for the lovely reference on ice thickness etc.

Looking at ice thickness up Jakoshavn and assuming an average retreat of 1.5 km or 1 mile a year for the next 50 years, it looks like Jakobshavn could raise sea level world wide by 150 to 300 mm.  (6 inches to 1 foot)  That would be by 2065.

What does the IPCC say the sea level rise for the world should be by then?

I believe the main contribution of JH to sea level was through its speed (and acceleration), not through its retreat. 15 km/year and more beats 1.5 km/year.

Yep, and advance the calving face 75 km inland and it should thin the drainage by 50%  That gets you 150 mm sea level rise.

[Espen]

Although I dont trust Modis Images alot, but we had a new moon and we can see the same behavior elsewhere in Greenland, but it seems Jakobshavn did something very serious:

If so, I bet this one is one of the top 3 within the last 5 years.

And well beyond the previous September 27 2014 max retreat point (southern branch)

[Espen]

Here is another version comparing September 27 2014 (previous max retreat) and August 15 2015:

Other calvings seen at least at Hagen Bræ and Upernavik Isstrøm probably a few more.

[A-Team]

seems Jakobshavn did something very serious, bet this one is one of the top 3 within the last 5 years.

Excellent spotting.

No Sentinel so far for the 14th, DMI is already on the 15th for N Greenland; Landsat due late tonight or tomorrow. The whole area looks unusual as the negative. I added an animated negative with slightly different processing.

To make a quick daily animation comparison, open DMI to the first image, copy image to clipboard, paste as new file in ImageJ. Ditto 2nd. Then make a stack. Crop and enlarge to 700 pxl width as new file (keeping small crop stack in case enhancement has to be discarded). Enhance contrast adaptively and in small stages with CLAHE. Save as animated gif, loop setting 0, 600 ms between frame. The key here is that DMI already has them fairly well aligned if it is the same satellite.

[Iceismylife]

Is that 1 mile of retreat in one day?

[TenneyNaumer]

Hey Espen, aren't the dates backwards on the blue gif (July 29 and Aug 14)?

[Laura Derrick]

There is some major sliding going on all over. Do you think that's partly tide-related?

[TenneyNaumer]

I'm just pulling this out of a hat, but I would say that tides have some effect, but they probably aren't enough to cause such large changes.

[Laura Derrick]

I'm just pulling this out of a hat, but I would say that tides have some effect, but they probably aren't enough to cause such large changes.

That makes sense. I've noticed that there's more fracturing off of fast ice during high tides, but I hadn't considered before that they might also affect glaciers until seeing a lot of activity this time. It would be interesting to look back and see if there's any correlation.

[solartim27]

I had noticed a weird surge into the bay on the 8/13 Modis, and noticed the front had advanced a good bit, I was wondering if the surge was related to the advance, or some other event I have not noticed.  It seems the surges take 2 - 3 days to exit into the bay, this one will be interesting to watch for.  Here is a gif of the area for 8/5, 8/13, and 8/15.

[TerryM]

Very nice catch Espen!


Laura
I've noticed a correlation in the past, but can't come up with an example off the top of my head.


Terry

[Andreas T]

have a look at the sequence of 17. 18. 19 July 2015 isn't that a lunar month earlier?
What surprises me, not having looked much at that area before, is how little the shape of the denser region of ice at the mouth of the fjord moves. Are there many stranded icebergs?

[nukefix]

have a look at the sequence of 17. 18. 19 July 2015 isn't that a lunar month earlier?
What surprises me, not having looked much at that area before, is how little the shape of the denser region of ice at the mouth of the fjord moves. Are there many stranded icebergs?

Yes, there's a shallower zone at the mouth of the fjord where the large icebergs get stuck for awhile.

[nukefix]

S-1 13.8 EW HH/HV 25m pixel size UTM Zone 22:

[A-Team]

Yes, there is a much studied terminal moraine from a previous glacial high stand at the mouth of the fjord by Illulisat where icebergs get stuck or scrape keel marks into the bathymetry. We are due for a stereo pair of Landsats today ... will it be cloudy or clear, the suspense builds.

Entity ID: LC80080112015228LGN00
Acquisition Date: 16-Aug-15

Entity ID: LC80080122015228LGN00
Acquisition Date: 16-Aug-15

[nukefix]

Not looking great for a cloud-free shot..

http://hotelarctic.com/om_hotel_arctic/webcam/

[Espen]

Yes, there is a much studied terminal moraine from a previous glacial high stand at the mouth of the fjord by Illulisat where icebergs get stuck or scrape keel marks into the bathymetry. We are due for a stereo pair of Landsats today ... will it be cloudy or clear, the suspense builds.

Entity ID: LC80080112015228LGN00
Acquisition Date: 16-Aug-15

Entity ID: LC80080122015228LGN00
Acquisition Date: 16-Aug-15

Relatively clear:

[A-Team]

Awright ... a few clouds but not so thick they can't be peeled off. The 2nd image shows band 8 at 7.5 m resolution. While clearly new territory, it is will take a bit (ie lunch time here) to compare to other dates and calculate the area and volume of ice calved. The third image is just the 15 m with a bit of context for folks co-registering different dates using the two fiducial rocks (ground control points).

This is path 8, row 11 if you are looking for near-identical geometry. The 8,12 has just been posted; the overlap miraculously includes the calving front.

[Iceismylife]

I had noticed a weird surge into the bay on the 8/13 Modis, and noticed the front had advanced a good bit, I was wondering if the surge was related to the advance, or some other event I have not noticed.  It seems the surges take 2 - 3 days to exit into the bay, this one will be interesting to watch for.  Here is a gif of the area for 8/5, 8/13, and 8/15.

Is there a convenient way to check the salinity of the water in those surges?  Are they fresher water from under the glacier?

[Espen]

As promised here:
https://forum.arctic-sea-ice.net/index.php/topic,154.msg60840.html#msg60840

we have several records involved:

1. I am pretty sure it is the largest calving seen in many years, if not the largest.

2. And a new record retreat.

[Espen]

And here is the confirmation of the new record retreat:

[Laura Derrick]

It's amazing also how much more exposed rock there is.

[Neven]

Thanks for the animations, Espen! I've put up a short blog post on the ASIB: Jakobshavn record retreat.

[A-Team]

Here is the comparison to 14 Aug 15. Some 28036 pink pixels calved off, an area of 28036 * 0.015 * 0.015 = 6.3 km

2

at 15 m resolution pixels. The first and third images show this over the latter and earlier image, respectively. There was a clue to some of this as noted in a post 2-3 days back but no clue as to the full extent observed.

If the ice is 1400 m thick, that works out 8.8 km³, a lot of ice! [These numbers had to be amended from the initially posted values, as Neven and Espen observe below.] 

Note it is imperative to use ground control points in comparing two images with different path,rows. The animation shows the rotation needed in the 14 Aug 15 image, LC80100112015226LGN00_B8 to get it registered with LC80080112015228LGN00_B8

[Espen]

A-Team I think 12,5 km2 is more likely?

[Neven]

Whoa, 124.6 km2! Is that for real? The last one in February was estimated at 7 km2 by Werther, and a couple of years ago NASA reported another 7 km2 calving (North branch).

Edit: thanks, Espen.

Does anyone have any other numbers of calvings in km2 to compare with?

[Espen]

The southern calving front is about 5 km wide and the cut is is about ½ the width so 5 x 2,5 = ~ 12,5 km²

And I am sure this is the largest single calving event seen since Jakobshavn went dual (southern/northern branch)?

[A-Team]

Oops, I used the wrong dimensions, throwing everything off. The revised area should  be 28036 pink pixels * 0.015 * 0.015 sq km per pixel for 15 m resolution band 8 Landsat or 6.3 km² for the area calved and 28036*0.015*0.015*1.4 = 8.8 km³ for the volume calved, assuming 1400 m average depth of ice. I will fix the original post to avoid later confusion.

I see few prospects for making this any more accurate: it is hard to tell what has calved but hasn't fallen away, is about to calve, and where the white is a vertical face or just a gnarly crevassed area at the front. Similarly for volume, it would be difficult to subtract off air in deep near-calving front crevasses.

None of this ice was floating so it all goes to sea level rise: 8.83 * 2.78 = 24.5 microns (0.0000245 meters, or 0.0245 millimeters, acording to this site:
https://climatesanity.wordpress.com/conversion-factors-for-ice-and-water-mass-and-volume/

How much does one Gigatonne of melted ice (1 km³ of water) raise the oceans?

The oceans occupy 361 million square kilometers ( 361 x 106  km²) of the Earth’s surface.

If one cubic kilometer of water (i.e., one gigatonne of water) is spread evenly over the entire 361 million square kilometers, the thickness of the new layer of water will be given by:

1 km³ / 361 x 106 km²  = 2.78 x 10-6 meters  = 2.78 microns.

That is, one cubic kilometer of water will add less than 3 millionths of a meter to the oceans!

Also, for the 2014 comparison, that date was September 28th. Landsat did not pass over Jakobshavn on the 27th. See earlier screenshot of 2014 dates at http://forum.arctic-sea-ice.net/index.php/topic,154.msg58765.html#msg58765

The path, row 10,11 back then don't match today's image so a rotation and translation will be needed to finalize the 'record' as needed (which might be gone as soon as tomorrow). These are in effect the first terms of the power series needed to warp one geometry onto another, ie it is the tangent spaces that are being co-registered.

28-SEP-14 LC80 10 011 2014 271 LGN00
 Sun Azimuth    178.10310829
 Sun Elevation    18.35757655
 Center Latitude 69.60641
 Center Longitude -50.87276

16-AUG-15 LC80 08 011 2015 228 LGN00
 Sun Elevation    33.9972875
 Sun Azimuth    173.78957895
 Center Latitude 69.60633
 Center Longitude -47.75851
 Date and time = 2015-08-16 T18:45:44Z

[Rubikscube]

It's amazing also how much more exposed rock there is.

The 2014 minimum occured in late September, so notice that the high ground was covered with fresh snow back then. When comparing to summer landsats from June, July 2014 futher up in the thread you have to look really close to find any significant difference at all. During a decade or so it will accumulate into a sizable amount, but from year to year retreat is still painfully slow.

I am under the impression that mega calvings like these usually occurs in June and July, so is it just a coincidence that this one is rather late? The "ramp and sill" image (Joughin et al 2014) posted by A-team previously this summer, indicates to me that we might have jumped over the bump in this latest calving.

[A-Team]

we might have jumped over the sill in this latest calving.

I like that concept. The idea is the glacier is coming over the sill very fast, over 50 meters/per day according to two accounts. It cannot bend rapidly enough to conform to the downward ramp bedrock and so is slightly cantilevered on the sill fulcrum out into 'space'. According to this notion, the event we have just witnessed amounts to the ice breaking off at the sill peak, no longer being strong enough to hang out like this anymore. (Someone, possibly sidd, suggested something similar at an Antarctic forum long ago.)

What happens next? One option is that the glacier comes forward again to where it was on the 14th, with this large calving pattern then repeated. There are six weeks of action left to the 2014 maximal retreat.

Another option is that Jakobshavn has entered a new regime of rapid repeat. Antarctic glaciers supposedly collapse irreversibly once on a retrograde bed (in part because warm sea water acts on a larger surface area).

We need to be cautious about calving statistics because of strong observational bias -- we simply miss a lot that goes on. As a practical matter, Sentinel hasn't been around very long, DMI Radarsat has limited resolution, Modis has contrast and resolution issues and our favorite, Landsat doesn't come by that often and when it does can encounter weeks of impenetrable clouds.

Since there does not exist a predictive theory of Jakobshavn capable of posting infill for observational gaps, we are discussing quite irregularly averaged-out behavior. The very fact that JI is the world's fastest/deepest ice stream has as a corollary that its essential parameters are the most difficult to observe experimentally.

For a very small investment, it seems feasible to post a monitoring team on site for the entire season.That could consist of heavily instrumented drone cameras as well as 24/7 videography from the last rocks (though that view is increasingly inadequate). It seems like we are missing a lot of easy opportunities to better understand this important glacier -- not to mention not bearing witness to some of the most incredible moments in nature.

[A-Team]

The image below rotates the 28 Sep 14 by the necessary 5.74º CCW that compensates for the path,row mismatch with the 16 Aug 15. The yellowish-green is the 2014 calving front, the greenish to the east the 2015. The two agree along a line passing by the last exposed rock in the SW (there is never calving below this line; it presumably is a wall of the south branch fjord).
 
The pink line represents 1 km (133.3 pixels =1000 m per km /7.5 pixels per m). The edge of the 2015 is 680 meters beyond that of 2014 as measured along this line.

Because of clouds, we don't know for sure that the 2014 really represents the previous record. However it is the furthest retreat we know of. Note how 2015 is a new record by a substantial margin across the entire calving front.

[AbruptSLR]

Here are references for Part I and II of a paper on the oceanic boundary conditions for Jakobshavn Glacier; followed by links to open access pdfs of the references:

Carl V. Gladish, David M. Holland, Aqqalu Rosing-Asvid, Jane W. Behrens, and Jesper Boje, 2015: Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14. J. Phys. Oceanogr., 45, 3–32, DOI: 10.1175/JPO-D-14-0044.1
http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0044.1

Abstract: "Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. This study collected hydrographic observations inside Ilulissat Icefjord and from adjacent Disko Bay between 2001 and 2014. The warmest deep Disko Bay waters were blocked by the entrance sill and did not reach Jakobshavn Glacier. In the fjord basin, the summer mean temperature was 2.8°C from 2009 to 2013, excluding 2010, when it was 1°C cooler. Despite this variability, summer potential densities in the basin were in the narrow range of 27.20 ≤ σθ ≤ 27.31 kg m−3, and basin water properties matched those of Disko Bay in this layer each summer. This relation has likely held since at least 1980. Basin waters from 2009 and 2011–13 were therefore similar to those in 1998/99, when Jakobshavn Glacier began to retreat, while basin waters in 2010 were as cool as in the 1980s. The 2010 basin temperature anomaly was advected into Disko Bay, not produced by local atmospheric variability.
This anomaly also shows that Ilulissat Icefjord basin waters were renewed annually or faster. Time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually, outside of summer. Fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month. In model simulations of the fjord circulation, subglacial discharge from Jakobshavn Glacier could drive renewal of the fjord basin over a single summer, while baroclinic forcing from outside the fjord could not, because of the sill at the mouth."


Carl V. Gladish, David M. Holland, and Craig M. Lee, 2015: Oceanic Boundary Conditions for Jakobshavn Glacier. Part II: Provenance and Sources of Variability of Disko Bay and Ilulissat Icefjord Waters, 1990–2011. J. Phys. Oceanogr., 45, 33–63, DOI: 10.1175/JPO-D-14-0045.1

http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0045.1

Abstract: "Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. Basin waters in this fjord exchange with neighboring Disko Bay waters of a particular density at least once per year. This study determined the provenance of this isopycnic layer for 1990–2011 using hydrographic data from Cape Farewell to Baffin Bay. The warm Atlantic-origin core of the West Greenland Current never filled deep Disko Bay or entered the fjord basin because of bathymetric impediments on the west Greenland shelf. Instead, equal parts of Atlantic water and less-saline polar water filled the fjord basin and bathed Jakobshavn Glacier. The polar water fraction was often traceable to the East/West Greenland Current but sometimes to the colder Baffin Current. The huge annual temperature cycle on West Greenland Current isopycnals did not propagate into deep Disko Bay or the fjord basin because isopycnals over the west Greenland shelf were depressed during the warm autumn/winter phase of the cycle.
Ilulissat Icefjord basin waters were anomalously cool in summer 2010. This was not because of the record low NAO index winter of 2009/10 or atmospheric anomalies over Baffin Bay but, possibly, because of high freshwater flux through the Canadian Arctic and a weak West Greenland Current in early 2010. Together, this caused cold Baffin Current water to flood the west Greenland shelf. Subpolar gyre warming associated with the NAO anomaly in winter 2009/10 was more likely responsible for the record warm Disko Bay and Ilulissat Icefjord basin waters of 2011/12."

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=4&ved=0CC8QFjADahUKEwiup7XD8K_HAhWD1SwKHTsFCXM&url=http%3A%2F%2Fdspace.mit.edu%2Fopenaccess-disseminate%2F1721.1%2F97579&ei=crPRVa6mPIOrswG7iqSYBw&v6u=https%3A%2F%2Fs-v6exp1-v4.metric.gstatic.com%2Fgen_204%3Fip%3D50.131.126.145%26ts%3D1439806323568686%26auth%3Dwtlmmij4kdsws3qvc22bppnuhp5difnv%26rndm%3D0.029521970489476912&v6s=2&v6t=9186&usg=AFQjCNHhmIz1KvpZu2aw90Mz_k8hGEonTA

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=5&ved=0CDkQFjAEahUKEwiup7XD8K_HAhWD1SwKHTsFCXM&url=http%3A%2F%2Fdspace.mit.edu%2Fopenaccess-disseminate%2F1721.1%2F97577&ei=crPRVa6mPIOrswG7iqSYBw&v6u=https%3A%2F%2Fs-v6exp1-v4.metric.gstatic.com%2Fgen_204%3Fip%3D50.131.126.145%26ts%3D1439806323568686%26auth%3Dwtlmmij4kdsws3qvc22bppnuhp5difnv%26rndm%3D0.23802496384177957&v6s=2&v6t=8225&usg=AFQjCNFcPC8WD4ocx1c8PVEnVrghxPKjZg

[Tor Bejnar]

...
None of this ice was floating so it all goes to sea level rise: 8.83 * 2.78 = 24.5 microns
...

I don't think this is quite true.  It would be true if the ice had initially been entirely above sea level.  Although none of this ice was floating, it was displacing water: 8-8ths before calving and 7-8ths afterward.  (But we'd have to know the bathymetry to calculate the volume of water displaced before calving.)  The thought experiment is to fully submerge an ice cube in a graduated beaker (and measure the volume), then release the ice cube and measure the apparent volume. (Then add another ice cube!)

[A-Team]

The calculation assumes full melt-out (which won't take long in Baffin Bay in August). In terms of displacing seawater, assuming quasi steady state, the ice stream will come forward and fully regain its former territory with uphill ice.

The 8.8 cubic km of ice volume converts to 2.1 cubic miles. Note the sill and ramp bathymetry here is not that well known despite a kazillion radar flyovers, making the assumed 1400 m depth a so-so assumption. Probably the best reconstruction is that of Morlighem, the final contours posted several months ago. The portion of the channel now buried in ice does not have a classic U-shaped cross section.

Next Landsat is a full week out:
 Entity ID: LC80090112015233LGN00
 Acquisition Date: 23-AUG-15

Radarsat comes by on a somewhat erratic schedule: 3, 10, 13, 17 so far in August. The images for the latter two dates are below.

Sentinel's schedule is also hard to anticipate: seven appearances so far in August at DMI but three of them [brackets] didn't make it far enough east to pick up Jakobshavn: [16], 13, 12  [09], 08, 06, [01]

However Terra and Aqua come by daily so progress can be followed despite mediocre resolution, provided it is not too cloudy.

[crandles]

Does this indicate depth of bedrock below SL


Estimating ice as 1400m thick grounded on bedrock at least 1000m below SL then volume above floatation is only a fairly small portion - about (1400-1000*8/7)/1400 = 257/1400 = 18.4%? This being a maximum percentage estimate. The average depth below sea level could be as high as 1200m in which case the volume above floatation could be tiny like 28.6m so possibly only 2% of calved volume is above floatation. VAF would cause a rise in sea level of 7/8th of its volume.
2% to 18% is quite a large uncertainty but a fairly small proportion.

Or is ice estimated to be 1400m above SL?

Or should it be calculated in some other way?

[Yuha]

A-Team, your calving area calculation seems to ignore the glacier movement. The glacier advanced a substantial distance over the two days as can be seen by looking at the markings in the ice just upstream of the pink area. My rough eyeball estimate is that the advance was about 75 m adding about 0.3 km² to the calving area.

[crandles]

The calculation assumes full melt-out (which won't take long in Baffin Bay in August).

AFAICS, I don't see any need for this assumption: if it is now floating, it is now displacing its own mass. (OK there is a slight problem re fresh ice in salt water but this is problem is tiny compared to other uncertainties like depth of water.)

[A-Team]

It has not floated in recent years, it rests on bedrock. Yuha is quite correct: forward motion of the glacier would add to the calved area.

However to do so, we need to pin down event timing relative to the Landsat shot on the 16th -- requiring someone to track down the UTC time stamp for the 2015-08-15 Aqua image Espen posted. On these, it is hard to compare quantitatively with the most recent one not showing the event (though we have a Landsat for August 14th taken at 2015:226:15:06:13.8590580, the August 16th is 2015:228:14:53:53.2749100

That's why I was inquiring over on the sea ice blog whether anyone had chased down the fjord webcam for surges. Ironically that is the same Holland authoring the two fjord water papers cited by AbruptSLR.

I located free full text for both up at ResearchGate -- is anyone able to pull out the vector graphics from Fig.1 of that pdf (and delete all the overlays, posting just a bathymetry jpg, perhaps using Inkscape)?
Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14
CV Gladish et al
http://tinyurl.com/qer3sfw

The Joughin bedrock profile should not be used. Despite the fall 2014 publication date of that excellent Brief Note, it only shows a single flowline based on 2008 bathymetry (which they felt was better than later DEMs).

I've re-located some of the Morlighem discussion -- sidd dug into the primary netCDF and I contoured it, some months ago. That is based on mass conservation and has quite a bit better resolution, showing bedrock troughs and hills. Thus to calculate volume, it would be better to sum over each pixel tower (bedrock depth to surface elevation * 225 sq m area) using numerical values in the original netCDF.

I'm not actually seeing the ramps and sills so often alluded to -- those become more complicated given cross-channel dimensionality. There has been a long series of poor practices in scientific articles on JI, not registering model features on contemporary Landsats, not providing kml files for flowlines etc, not specifying map projection, not working in GIS layer mode, not providing anything more than auditorium quality graphics, covering critical data with obscuring text, not utilizing journal supplemental, on and on. Details apparently don't matter when working in sandboxes (models) having no long-term interest. I cannot think of another area of science where this would have been tolerated.
http://forum.arctic-sea-ice.net/index.php/topic,1165.0.html

http://forum.arctic-sea-ice.net/index.php/topic,154.msg45799.html#msg45799

[Espen]

I have to make a confession and a correction.
Somehow I archived the September 27 as one from 2014, but the fact is it is from September 27 2013
(A-Team: "Landsat did not pass over Jakobshavn on the 27th" thanks for making me suspicious).
The interesting thing now is when was the previous max. retreat prior to the August 14-15 2015 calving?
Was it September 27 2013 or September 28 2014? Overall I would say 2014, but when only watching the southern branch I am not so sure?
Can you tell the difference?

[A-Team]

No problem; it is interesting to see them so similar. Does the calving front sequence Neven is showing have the updated calving front for 2013/14? Have you tried reverse image search to try to properly credit the original calving front graphic, tin eye, imageraider, google?

The 2013 is LC80 08 011 2013 270 LGN00 which is a different path,row geometry from the LC80 10 011 2014 271 LGN00 2014 max retreat so a rotation will be necessary to compare the band 8's.

Real-time science is error-prone; we really should finish collecting all the available data first and then re-visit the quantitative analysis. It's helpful though to have input from many perspectives. (Meanwhile our first efforts will be picked up and irrevocably amplified across the web!)

We should also be checking Twitter to see if someone took footage of the event, recalling tourist footage posted in June. I have little doubt that scientific teams, or at least their equipment, is out there on the easternmost rocks.

There is an extensive seismic array set up on Greenland -- glacier calving sets that off (as the ice stream reels from a big calving loss). I haven't used this but believe it is real-time public domain. It could help narrow the time bracket for this event.

Someone needs to measure August 2015 velocities if we want to make a glacier advance correction ... that velocity will be quite uneven along a perpendicular to flow lines. We have posted previously all published velocity maps including ones from approved dissertations back somewhere in this forum but those won't be applicable to a 2015 event.

The other peculiar feature of this event is the off-center lobe of maximal calving. Somewhere I painted on the distinct contributing sources to the calving front. The Jakobshavn Isbrae proper is the ice source only for the northern fifth or so. The ice calved in the lobe originates nearby, angling in from the southern flank perhaps 20 km back. This ice could be warmer at depth -- there are no experimental temperature transects. Alternatively, this region is moving slower so just slower to replenish than the Isbrae proper.

What defines an 'event' anyway? Jakobshavn actually calves 24/7/365, not continuously perhaps but if ice discharge volume were binned into hourly intervals, the plot vs day of year would rarely scrape zero on the graph. This graph (which we don't actually have but might be estimated from the fjord web cam freeboards) is quite seasonal and subject to bin surges that might last for an hour to several days as an initial big calving triggers instability on its flanks and further back.

An event might be objectively defined as the rolling bin average continuously exceeding two std dev of the seasonal norm, with flanking ramp-ups thrown in. We don't know if this event has finished or only paused. We can't determine whether the Modis on the 15th has the same calving front position (modulo glacier advance) as the Landsat on the 16th. The Landsat shows two significant areas 'on the verge' of calving. The 'Chasing Ice' event here lasted 75 minutes.

Terra just came in for the 17th: too cloudy to determine the calving front.

I've collected some more Landsat trivia. EarthExplorer is not posting images in the order taken, who knew? The LC80080122015228LGN00 from yesterday had a stop time of 14:54:48.93 whereas LC80080112015228LGN00 had a stop time of 14:54:25.04 yet is listed second. Landsat is collecting data as nadir line scans, so in theory these two should be identical on the overlap (unless some difference in processing occurs based on image centers).

LC80080122015228LGN00
 Start Time  14:54:17.16
 Stop Time  4:54:48.93

 Center Latitude    68°16'46.70"N
 Center Longitude    49°27'10.01"W

LC80080112015228LGN00
 Start Time 14:53:53.27
 Stop Time  14:54:25.04

 Center Latitude    69°36'22.79"N
 Center Longitude    47°45'30.64"W

[Sourabh]

A-Team,

Sorry to ask a stupid (noob) question. Last year also, I was confused on the same image.

I am finding it difficult to visualize carving on the animation you posted (14 vs 16th). 16th Image looks better (solid ice sheet) and it seems lot of slush in 14th. Why is that? Did ice( water) refroze on 16th?

[A-Team]

difficult to visualize carving on the animation you posted (14 vs 16th)

The interpretation of Landsat images is seldom clear to me over an entire scene, in part because it is looking straight down and not quite natural color whereas helicopter shots are helpfully oblique. In theory it would help to drape the Landsat over a hill-shaded DEM (if we had a really recent one).

The debris in front of the calving front -- proglacial melange -- provides a clearer boundary to the south than in the northern shore (of the south branch). In fact, it is not at all clear without looking at movement in 5-6 sequential images what is going on in the upper corner. It may help if a Sentinel radar image emerges for a relevant date. It's never a good idea to go with 'it's obvious to me' ... better to find a second line of independent support.

We could retrieve online temperature records -- Holland has/had an automatic weather station on the northwest rocks. Illulisat would also be reporting but that might be moderated by the surrounding bay. I don't believe there is much re-freezing going on (based on youTube events) once the ice hits the water this time of year. The extreme depth of the calving front means extreme turbulent mixing of ocean waters. These have far too much heat content (relative to ice volume) to freeze unless stratified. The ice takes its sweet time to melt in the fjord but drops out quickly once in Disko Bay.

In some instances (like the north shore depression where we went around in circles forever), the matter was ultimately resolved by a huge level zoom luckily provided by a Google Earth base image. Landsat-8 at 15 m is great to have but it's borderline relative to the intrinsic scale of ground features (crevasse width). Worldview 3 is something like 0.5 m but we don't have the budget for access.

[iwantatr8]

A-Team,
Do you have the wider view difference between the 14th and the 16th showing the bend ( you posted a wide view on the 14th #806)?.  I say this as flicking between the Terra images on worldview seems to indicate that something may have happened further upstream. 
There is a hole in the cloud cover for the 17th and a feature starting to appear at the north side of the southern channel on the 15th and 16th may indicate something astonishing for the 17th August.  I might well be wrong but it looks like there may have been a significant further retreat.

[A-Team]

Can you overlay an arrow or asterisk?

Yes indeed, there is a lot to look at on the 14-16 images beyond the calving front story. If this is the start of an historic unraveling, then we want to documenting as much as we can (before moving to higher ground  )

It is problematic animating very much of these images at 15 m much less 7.5 m because the forum software chokes on large/wide files. Also it might be better to use the 16th vs an earlier image with the same geometry. I have LC80080112015180LGN00 'in stock' but day 180 vs day 228 raises other issues. It looks like LC80080112015212LGN00 might work...

[iwantatr8]

What I am looking at is attached I'm looking at the 721 terra image.

The first image from the 17 and the second from the 16th.  on the 16th you can locate the feature as being just to the left of the melt lake  beyond the bend, and as a slight lightening that connects the calving face with the top of the bend.

On the 17th the previous calving face is hidden but the melt lake beyond the bend is clearly visible, but the feature has grown to cover most of the glacier and look like a new calving face but this would be some km upstream of the existing face.