Neven;
I am aware of that, but this year hardly no snow cover in the area, and the blue ice indicating melting.
Espen: Has this happened this early before? I seem to remember a similar melting in April but never March.
Spring cleaning Ilulissat Icefjord;
A big of piece of ice that was resting on the southern shore is on the move:...
Sigmetnow,
As I recall, the text is in a layer, so you got to flatten the image, I am pretty sure that will work!
Daily animations from Ilulissat isbrae:
http://sermitsiaq.ag/icecam/ (http://sermitsiaq.ag/icecam/)
The view from the webcam at Hotel Arctic in Ilulissat is really worth it today.Hi bernard,
The view from the webcam at Hotel Arctic in Ilulissat http://www.hotelarctic.com/files/webcam/webcamshot.jpg (http://www.hotelarctic.com/files/webcam/webcamshot.jpg) is really worth it today.
A week ago the bay was mostly open water except for the impressive bergs run aground in the background. Today it's almost completely covered with a chaos of chunks of all sizes.
Enjoy it now in the calm sunset. Image refreshes every five minutes or so, you can really see all this stuff moving around.
Position of the hotel (and webcam) http://www.geonames.org/8520900 (http://www.geonames.org/8520900)
I’ve put a larger version of the map in photobucket. Hope it is useful.
We know there are links, for example, in the ocean temperatures that run down the west coast of Greenland which are very warm at the moment. Exceptionally warm!
@Artful Dodger thanks for the welcome!
For the record I'm not related whatsoever with Hotel Arctic, and (unfortunately) never been to Ilulissat
Yes its generic google earth sat view of Jakobshavn.Which appears to be really old, like 5+ years old based on the position of the calving front.
Je suis triste pour la fonte du Groenland et les Hautes-Alpes.I tried today to figure the size of the last week calving in Jakobshavn Isbræ by comparing its volume to the Hautes-Alpes Glacier Blanc, which we still find here very impressive despite its spectacular recent retreat. According to http://en.wikipedia.org/wiki/Glacier_Blanc (http://en.wikipedia.org/wiki/Glacier_Blanc) the area is a little more than 5 km² for a maximum depth of 250m. Which gives a maximal volume of a little more than 1 km3 of ice.
Hi, guys.
Do you have a feeling that we are hijacking Espen's thread a bit? ;-)
BTW weather is in for a decade of freeze over there now. Circulation changed…
You mean because of the Cold Pole that shifted over Greenland?
Neven, since I gather 10-day NCEP/NCAR summaries, I call these decades. I guess that's confusing...I don't mean years.
And confirmed; about 1,2 km2 on the NE side of the main calving front.
Still more than 9 km2 to go to get beyond July '12.
A 1 mm movement today, southern front!
1 mm represents 1 km at Modis 250M ;)
What happened to Web cam at Hotel Arctic?
A raven with digestive problem?
I do not see this 1 km, change, nor do I see the icebergs that should have been generated by such a change. What am I missing? :-\
Another big calving (compare days 196 and 200).
The calving front has now retreated beyond last year's position, I think.
Werther, does your CAD agree?
I did put the links here ?
https://forum.arctic-sea-ice.net/index.php/topic,270.msg14150.html#msg14150
This is the link :
http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004097/ (http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004097/)
The image with jakobshavn is after this image, I took the highest resolution and did a crop on it + jpg high compression :
So that makes the retreat about 19 km over the past 12 years. About 1.5 km/yr on average.
How long can this continue? Do we expect acceleration or slow-down?
I haven't checked IPCC AR5 on this yet, but maybe other people here know?
Bedrock map of Jakobshavn :
I did put an arrow where I guess the front of the glacier is, or is it where the sea is viewed !?
You can click on the image to enlarge it !
Jakobshavn,waiting for your next move:
As mentioned above the "New Front" development is seen on this NASA image from yesterday
It is not a new calving front, but it does represent a steepening of the slope, enhanced crevasse and serac activity. This is close enough to the front to potentially not be stable without retreat to it. We generally do not see such a narrow embayment develop on this glacier, so if it does retreat to that point the lateral extent will be greater.
It is not a new calving front, but it does represent a steepening of the slope, enhanced crevasse and serac activity. This is close enough to the front to potentially not be stable without retreat to it. We generally do not see such a narrow embayment develop on this glacier, so if it does retreat to that point the lateral extent will be greater.
Since this enhanced crevasse and serac activity is occurring beyond the existing calving front, should we expect this kind of activity to expand as the calving front retreats?
Would you be able to plot the ice thickness at which it would be possible to float at?
There's always Hotel Arctic webcam at Ilulissat, which may be north of where you're looking. It's not showing anything exceptional right now.
http://www.hotel-arctic.gl/om_hotel_arctic/webcam/ (http://www.hotel-arctic.gl/om_hotel_arctic/webcam/)
There's always Hotel Arctic webcam at Ilulissat, which may be north of where you're looking. It's not showing anything exceptional right now.
http://www.hotel-arctic.gl/om_hotel_arctic/webcam/ (http://www.hotel-arctic.gl/om_hotel_arctic/webcam/)
That is way away from where the action is (only about 45 km).
Just puzzled to where all that ice went? My estimate is 5 - 6 km2 of glacier ice went down the drain!
@nukefix any idea when such Sentinel-1 images will be available?The satellite in in commissioning-phase that should take until late September or so. See mission status for updates:
Ten Cubic Kilometers of Ice Lost From Jakobshavn Glacier in Less than One Month
How large is a cubic kilometer? Think of something the size of a mountain. Now multiply that by ten and you end up with a veritable mountain range. Think of it. An entire mountain range of ice. That’s a good rough comparison to the volume of ice lost from just a single Greenland glacier over the course of a mere 26 days from May 7 to June 1 of 2014.
For according to reports from expert sea ice observer Espen over at the scientist and ice researcher camp that is Neven’s Arctic Ice Blog, about 7.5 square kilometers over an ice face about 1,300 meters tall (when including the above and below sea level ice front) shoved off from the great Jakobshavn Ibrae glacier during the past month. It was a period of time well before peak Greenland warming and one that featured a collapse of ice into the heating ocean even larger than the epic event caught on film during the seminal documentary Chasing Ice.
And what lies beneath from Hughes(2014) doi:10.5194/tcd-8-2043-2014 (open access)
"Gogineni Gorge" fig14 attached
I like it
That is a nice paper, but the Byrd comparison is probably better discussed in one of the Antarctica threads.
sidd
How much km2 are we talking now? Is this picked up anywhere? NASA?
Very sad that Robert Scribbler and here seem to be the only places on the WWW that seem to have caught onto the story. No search engine as of yet can find anything else about this particular calving.
Be aware! We have have not reached the maximum retreat point of September 2013 yet, at some points yes but not depth wise :
Please click on image to start animation!
Be aware! We have have not reached the maximum retreat point of September 2013 yet, at some points yes but not depth wise :
Please click on image to start animation!
Thanks, Espen. I don't keep an eye on this, and so I didn't know about the retreat point.
Shared Humanity, yes it looks like the whole plateau is on the move, I don't really know what is happening, but there must be a lot of stress and re-stress in area as a whole, and there is more to come over next few days, that can be seen when analyzing the images.
Looks like NASA has picked up on the recent calving.
http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&eocn=home&eoci=iotd_readmore (http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&eocn=home&eoci=iotd_readmore)
Many thanks for all the nice topography maps everyone. I kind of share your concern SH, perhaps first and foremost because of the developments we have seen in the Northern branch during recent years, a branch which also seems to have a quite limited depth. My assumption after seeing the newst maps, is that it wouldn't be a very big surprise to see a third branch slowly emerge.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi58.tinypic.com%2F20as8cj.gif&hash=0edd4e2e3e1cb14af8241e77f617e97e)
However, what really frighten me is this.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi57.tinypic.com%2Ffpcjmo.gif&hash=d73e5654db62594e9252ac3d36d07397)
Hopefully, and probably, it is going take several decades before Jakobshavn splits into multiple branches that each are capable of penetrating several hundred kilometers into the Greenland ice sheet, but the fact that all these canyons exist would suggest pretty strongly that there have been numerous fast moving glacial outlets right in the middle of Greenland during previous meltdowns. It strikes me though, that most of this vast network of canoyns is excluded from more detailed topography maps of Jakobshavn and doesn't seems to be a videly discussed issue. Is it just too far into the future?
It seems to me that the potential collecting area is higher for Jakobson !? On the geological map of Zachaeria it is not clear if it is linked to the inside of Greenland, can you tell us what are the volume potential of each of them ?
Any idea what the line to the northand inland of Jacobshavn is? Melt water channel? Seemed to form in a week, last clear day there was 6/2.
Really good images for calving and retreat documentation, I thought the intervals (12days) would be shorter when it is a so called Supersite?It will be imaged from both ascending and descending orbits every 12 days, it's too early to tell what will be the separation in days between the ascending and descending acquisitions.
Espen, could you post the June 24 image on its own and without overlapping titles?
It shows the shapes of the ice surface with spectacular clarity.
Espen, could you post the June 24 image on its own and without overlapping titles?
It shows the shapes of the ice surface with spectacular clarity.
NB! This is a cut-out of the original image 4MB.
Calving front update:
The image below show where the calving front was on September 27 2013 (red line) and June 24 2014 (yellow line).
At some points Jakobshavn retreated beyond the Sep. 27 2013 calving front, but still behind 2013 at the eastern main gate.
Right, strange flow pattern in the vicinity, topography is a bit of a puzzle. However ordinary google map has a great series of zooms here (once you're sure you're zooming on the right object, the north fork has retreated a lot since this imagery. The melt lake is very black in Landsat today but by clicking on it with the color wand tool, other lakes prove just as black (while most are classic blue). Click if the animation doesn't start.
[ Wow - good detective work there, thanks - it's a melt lake then!. that would explain why it grew so quickly. As you say, the topography a bit unusual there/quote]
Here we go, perspective DEM from TerraSar. May or may not be some degree of vertical exaggeration. Not sure of the date either. North branch is clear locatable; more extreme topography than i would have guessed from the nadir view of Landsat. It's not so easy to be sure the melt lake is in the pocket though.
I thought this was just a melt pond as well and that it would rather be caused by an emerging nunatak. Either way it is kind of strange looking.
I thought this was just a melt pond as well and that it would rather be caused by an emerging nunatak. Either way it is kind of strange looking.
This could be a melt pond but I do not believe this is the case either. I think what we are seeing is open sea, the actual surface water of the shallow basin that sits underneath this portion of the ice sheet. The ice sheet on this particular portion of the north branch has completely melted away. This is why this area is as dark as the water in the open fjord. We are not looking at a shallow melt pond or lake. We are looking at open sea. While it is certainly shallower then the fjord, the topography map suggests this water is perhaps 100 meters deep, maybe deeper.
I thought this was just a melt pond as well and that it would rather be caused by an emerging nunatak. Either way it is kind of strange looking.
This could be a melt pond but I do not believe this is the case either. I think what we are seeing is open sea, the actual surface water of the shallow basin that sits underneath this portion of the ice sheet. The ice sheet on this particular portion of the north branch has completely melted away. This is why this area is as dark as the water in the open fjord. We are not looking at a shallow melt pond or lake. We are looking at open sea. While it is certainly shallower then the fjord, the topography map suggests this water is perhaps 100 meters deep, maybe deeper.
Why wouldn't ice be pushed into this below sea level area? Perhaps it is but it keeps melting due to warm water is the only reason I could suggest. This seems unlikely to me without there being known geothermal activity but then I wouldn't really trust my intuition given my lack of knowledge.
I have wanted to begin a review of Zacharia Istrom (sic) using the same images because Espen is certain that this glacier has far more sea level rise potential. If Espen feels this way, I am certain I do as well. I simply cannot tear myself away from this monster.
I absolutely do not believe this is an emerging nunatak.
Steve Bloom,
I have seen no papers. The information available seems difficult to come by. I have searched the internet for historical records and have found a few in the past but I have not been able to find them now. There is a book by John Muir, Travels in Alaska but I do not own a copy. There seems to be only bits and pieces of information between 1794 and the mid 1800s available. What is clear is that the ice was there in 1794 when Captain Vancouver visited the area and the it was gone not very many years later.
The Tlingit people who lived in the area had an oral history of the area at the time which is mentioned on the National Park Service website link in my earlier post.
The Neoglacial landscape of the Huna Tlingit homeland in Glacier Bay is recreated through new interpretations of the lower Bay's fjordal geomorphology, late Quaternary geology and its ethnographic landscape. Geological interpretation is enhanced by 38 radiocarbon dates compiled from published and unpublished sources, as well as 15 newly dated samples. Neoglacial changes in ice positions, outwash and lake extents are reconstructed for c. 5500―200 cal. yr ago, and portrayed as a set of three landscapes at 1600―1000, 500-300 and 300―200 cal. yr ago. This history reveals episodic ice advance towards the Bay mouth, transforming it from a fjordal seascape into a terrestrial environment dominated by glacier outwash sediments and ice-marginal lake features. This extensive outwash plain was building in lower Glacier Bay by at least 1600 cal. yr ago, and had filled the lower bay by 500 cal. yr ago. The geologic landscape evokes the human-described landscape found in the ethnographic literature. Neoglacial climate and landscape dynamism created difficult but endurable environmental conditions for the Huna Tlingit people living there. Choosing to cope with environmental hardship was perhaps preferable to the more severely deteriorating conditions outside of the Bay as well as conflicts with competing groups. The central portion of the outwash plain persisted until it was overridden by ice moving into Icy Strait between AD 1724―1794. This final ice advance was very abrupt after a prolonged still-stand, evicting the Huna Tlingit from their Glacier Bay homeland.
As we brace for tomorrow's hi-res Landsat (which might not be online until Friday -- and even then might be clouded over), we might set some rules governing 'records'.
It is not enough for the calving line to retreat past the all-time record set on 20 Sep 13. Although mildly remarkable with 70 more days to go in the retreat season, just going slightly beyond last year is not even keeping up with the multi-year trend: an additional km of retreat is the new normal.
Indeed, slightly more would still be business as usual since the rate of retreat may be accelerating. Thus we shouldn't trouble our colleagues on the ASIB with news on this little glacier until the retreat is a second km beyond the first km expected.
However that model won't be applicable to any other glacier in Greenland as the others lack the overdeepened bed channel. In some ways, GRACE trending (mass balance from gravity) may provide the best overall view of Greenland's total contribution to sea level rise.Repeat-pass altimetry provides a much higher resolution and reaches pretty close to the margin, so I'd combine the two.
That incredible low angle image yesterday with perfect shadows got me motivated to find the others. It is quite convenient to get Landsat metadata in bulk at http://landsat.usgs.gov/consumer.php (http://landsat.usgs.gov/consumer.php) and then sort through the nuisance xml (that nothing can parse) to find the low sun angle scenes. Discarding the cloudy ones over JI gives the table below for 2014. Snow cover can be an issue with earlier dates.
I've attached a region flanking the upper ice stream where shadowing contrast reveals adjacent ice sheet to the north being seriously distorted by the out-competing ice stream. Note too the subtle ribbing farther up. It looks to me like much older relic features are being over-written but not quite obliterated by the strain rate tensor operative in more recent years.
(do I believe interior sea level bedrock depiction?)
....
As car #2, I had to slow down and speed up the whole while because I could not pass nor reach the AK-47 in the back seat.
....
Here is another feature from digiglobe hi res, to the east and slightly to the north of the end of the south branch of the JI. The drainage here shows a couple of things going on, including streamlets seemingly confined to linear troughs of ice compression waves. The surface is so flat that the slightest change in elevation can give rise to extended, complex water features.
Beautiful work A-Team!
Is it wildfire smoke that is visible across Greenland from Jakobshavn to Kangerlussuaq today? If so, (the resulting ash/soot) couldn't be good for albedo...
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(
They are focusing on lining up multinationals for exploiting the emerging natural resources.
(I wish this wasn't actually true.)
Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014
Here's a zoom showing individual pixels, the pixel-size is 10m in both range and azimuth. Note that this zoom shows a tiny corner of a 480 megapixel (per polarization) datatake. In other words, S-1 will provide huge area coverage while other SARs should be used when very high resolution is desired.Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014Hope they will come up with better resolution?
My question: with hundreds of academic researchers on the Greenland payroll, why do I have to prowl internet blogs for proper workup of the (very expensive) data? These radar overflights began in earnest in 1993.
Nukefix, that is fantastic news. Can you share the link to these Sentinel images ... or does one have to go through a klutzy map search interface?It is necessary to go to https://senthub.esa.int/ to do the download. Just draw a rectangle over Greenland and press search. The product in question is:
Do we know what this is? (red encircled):
Here is a follow-up on the growth of the dynamic influence area of Jakobshavn Isbrae. It is poaching ice sheet input from neighboring ice sheds, as well as implicating more ice sheet east towards the summit.What altimeter is that based on?
The land-terminating glaciers don't get much attention on Greenland but are significant because impacts of overall melting can be disentangled from the effects of warming ocean water (eg Irminger Current) on the bases of marine-terminating glaciers.
Could be completely unreliable (Modis), but still?:
Indications of collapse of side wall (northern) at the southern branch
And that could eventually result in a faster flow?
A place in forum history? Still 6 weeks left in the calving season.
Yes Steve, that could be, but ASAR also show some changes:
Yes Steve, that could be, but ASAR also show some changes:What is ASAR? Certainly not the Envisat ASAR as that satellite is dead and tumbling..
Yes Steve, that could be, but ASAR also show some changes:What is ASAR? Certainly not the Envisat ASAR as that satellite is dead and tumbling..
Nukefix, "Note in the lower right corner how differentiation between the ice-stream and ice melange with icebergs can be hard.", is it not more due to the viewing angle?Even with the same viewing-angle the ease-of-differentiation depends on environmental conditions (season). Higher resolution would make the task easier but this is what we are stuck with. The use of textural measures might make the task a bit easier for a human operator.
Feature-tracking with SAR works, lets hope that the S-1 coverage will cover more of Jakobshaven in the future.
No retreat record ... calving some big ones but not quite keeping up with icestream advance. We have no idea on whether a discharge volume is being set -- I can try once again to see if feature tracking over time is possible from Landsat (to see how seasonal velocity compares to past years).
As suggested we had some calvings since last update, Aug. 27 2014 is almost at the maximum retreat set Sep. 27 2013, the northern branch is definitely in the retreat zone. The last frame in the animation below is Sep. 27 2013:
That would be a big plus. How does radar do on snowy scenes though? Seems like surface roughness takes up quite a bit of channel space.Snow and snow wetness affect the level of backscatter. However, feature-tracking is based on tracking visible features (crevasses), so changing the level of backscatter should not matter that much especially if suitable pre-processing is used to mitigate differences in backscatter-levels.
Prasad Gogineni and his henchmen have a paper out on subglacial topo under Jacobshawn (and Byrd, in Antarctica), including juicy ice layer data from CRESIS.
doi: 10.3189/2014JoG14J129
Mr. A-Team should be all over this when he reappears.
sidd
Interesting: the south branch advanced quite a lot while the north branch did not advance at all during this period
'Since 1990, several attempts have been made to sound Jakobshavn and other fast-flowing glaciers, with very limited success. Fully coherent radars operating over the frequency range 1–450 MHz are used for these measurements (Gogineni 2001, 2012; Dall 2012; Morlighem 2014). We first succeeded in sounding Jakobshavn Isbræ ... in 2005.'Chasing this down, 'Dall 2012 P-band radar sounding in Antarctica' concerns a threat from satellite radar, which could provide more comprehensive coverage of big continents if only the surface clutter issue could be resolved. That radar (ESA Polaris) on airplanes not only reached bedrock in 3300 m ice on the Greenland summit ridge (possibly detecting basal melt as well) in 2008 but also obtained spectacular results (images below) in Antarctica using a remarkably effective enhancement (first derivative of nadir return power) to better get at internal stratifications.
Fahnestock, Scambos, Kinger: The high radiometric resolution [12 bit] of Landsat 8 enables one to track subtle patterns on the surface of the ice sheet, unique at spatial scales of a few hundred meters, between images separated by multiple orbit cycles. In areas with significant dynamic topography generated by ice flow, this requires use of simple spatial filtering techniques first applied by Scambos 1992 [free full http://tinyurl.com/loveunb (http://tinyurl.com/loveunb)].
The result is densely sampled maps of surface motion that begin to rival the coverage available from SAR speckle tracking and interferometry. Displacement accuracy can approach one tenth of a pixel for reasonable chip sizes [small chunk of large image] using conventional normalized cross-correlation; this can exceed the geolocation accuracy of the scenes involved, but coverage is sufficient to allow correction strategies based on very slow moving ice.
S-1 6.12.2014 in UTM22/WGS84, full-resolution jpeg. Looks like the southern side of the southern branch has retreated some more.
Thanks Espen! I can keep producing S-1 in UTM22 as they come in order to make a time-series..
I have trouble getting the forum to accept my attachments...perhaps they are too big? Does anyone know what the limits are?
I have trouble getting the forum to accept my attachments...perhaps they are too big? Does anyone know what the limits are?
we could possibly still end up worse than Pfeffer et al assumed, if Rignot is right with his worst-case judgement. Or would he be too pessimistic?Seems right on-target to me, given the adverse developments lately in Greenland and need to apply the Precautionary Principle in any event.
https://agu.confex.com/data/handout/agu/fm14/Paper_26038_handout_952_0.pdf
Thermo-mechanically coupled modeling of high elevation regions of the Greenland Ice Sheet
A Sommers et al
http://www.williamcolgan.net/pubs/S0012821X14006360.pdf
Basin-scale partitioning of Greenland ice sheet mass balance components (2007–2011)
M.L. Andersen et al
Andersen paper confirms Enderlin et al, doi:10.5194/tc-7-1007-2013 in that surface mass balance now dominates in GreenlandThat doi is an interesting paper in its own right but you may have intended her Feb 2014 doi:10.1002/2013GL059010; note the Nov 2014 B Csatho PNAS paper (free full, reviewed on another forum) has SMB at about half. There's yet more coming per AGU 2014.
Enderlin, E. M., I. M. Howat, S. Jeong, M.-J., Noh, J. H. van Angelen, & M. R. van den
Broeke, 2014. An improved mass budget for the Greenland ice sheet. Geophys. Res. Lett.,
866-872, doi:10.1002/2013GL059010
Annual measurements for 178 outlet glaciers reveal that, despite widespread acceleration, only 15 glaciers accounted for 77% of the 739 ± 29 Gt of ice lost due to acceleration since 2000 and four accounted for ~50%. Among the top sources of loss are several glaciers that have received little scientific attention. The relative contribution of ice discharge to total loss decreased from 58% before 2005 to 32% between 2009 and 2012. As such, 84% of the increase in mass loss after 2009 was due to increased surface runoff. These observations support recent model projections that surface mass balance, rather than ice dynamics, will dominate the ice sheet's contribution to 21st century sea level rise.
Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics
BM Csatho et al www.pnas.org/cgi/doi/10.1073/pnas.1411680112 (http://www.pnas.org/cgi/doi/10.1073/pnas.1411680112)
We estimate a mean annual GrIS mass loss of 243 ± 18 Gt·y−1, equivalent to 0.68 mm·y−1 sea level rise (SLR) for 2003– 2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004–2006, followed by a gradual decrease balanced by accelerating SMB loss...
High sensitivity of tidewater outlet glacier dynamics to shape
EM Enderlin et al doi:10.5194/tc-7-1007-2013 www.the-cryosphere.net/7/1007/2013/ (http://www.the-cryosphere.net/7/1007/2013/)
http://cci.siteturbine.com/facultystorm/profile/cv.php?profileId=933 (http://cci.siteturbine.com/facultystorm/profile/cv.php?profileId=933)
... for glaciers with similar discharge, the trunks of wider glaciers and those grounded over deeper basal depressions tend to be closer to flotation, so that less dynamically induced thinning results in rapid, unstable retreat following a perturbation.... varying the bed topography within the range of observational uncertainty can result in either stable or unstable retreat due to the same perturbation.
Try to reduce the picture (700x700 pixel is enough)?Well, they are already crops of ~20000*20000 pixel images so going to that extent would be really unsatisfactory..
Change the extension ?
already cropped way down from 20000 x 20000 pixelsnuke, could you conveniently post some of those orange quicklooks like Wipneus has been posting? Way lower resolution but still possibly of interest. http://forum.arctic-sea-ice.net/index.php/topic,176.msg42626.html#msg42626 (http://forum.arctic-sea-ice.net/index.php/topic,176.msg42626.html#msg42626)
"Nonetheless, we do measure velocities >50 m/day at times in the summer of 2012 (not shown in our paper). We have extended the TSX [TerraSAR-X satellite] record through 2014 and find that, when comparing the speeds at the same point, peaks speeds in July 2014 are considerably slower than the 2012 peak by about 2-3 km/yr [~17% slower] . So any references to faster speeds in 2014 should be removed (this in no way detracts from the quality of the results)."
Our objective is to map dynamic provinces and investigate dynamic changes in Jakobshavn Isbrae. We use an approach that combines structural glaciology and remote-sensing data analysis, facilitated by mathematical characterization of generalized spatial surface roughness that provides parameters related to ice dynamics, deformation and interaction of the ice with bed topography.http://www.ingentaconnect.com/content/igsoc/jog/2014/00000060/00000223/art00002 (http://www.ingentaconnect.com/content/igsoc/jog/2014/00000060/00000223/art00002)
The approach is applied to derive time series of elevation and roughness changes and to attribute changes during rapid retreat. Different dynamic types of fast- and slow-moving ice can be mapped from ICESat (2003–09) and ATM data using spatial roughness characterization, validated with ASTER and bed-topographic data.
Results of comparative analysis of elevation changes and roughness changes indicate surface lowering of 10–15 m/yr between 2004 and 2009 but no change in surface roughness and dynamic types. These findings are consistent with a front retreat as part of a fjord-glacier cycle or following warming of fjord water and with climatic warming, but not with an internal dynamic acceleration as a cause of rapid retreat. Relationships to changes in basal water pressure are discussed. All glaciodynamic changes appear to have initiated near the front and propagated up-glacier.
Supraglacial melt channel networks in the Jakobshavn Isbræ region during the 2007 melt season
DJ Lampkin and J VanderBerg
free full: http://onlinelibrary.wiley.com/doi/10.1002/hyp.10085/full (http://onlinelibrary.wiley.com/doi/10.1002/hyp.10085/full)
Supraglacial channels are an important mechanism for surface water transport over the ablation zone of western Greenland. The first assessment of the spatio-temporal distribution of surface melt channels and their relationship to supraglacial lakes over the Jakobshavn Isbræ region of Western Greenland was analysed using Landsat during the 2007 melt season.
A total of 1188 melt channels were delineated and show an increase in the number of melt channels throughout the season, reaching a peak on 9 August. Water-filled melt channels advanced to a maximum elevation of 1647 m on 9 August and attained a minimum average slope of 0.009 on 8 July. The ablation zone demonstrates two hydrologic modes, where crevasse and moulin terminating channels dominate at elevations <800 m and higher-order channel networks >800 m. Development of higher-order networks is interrupted by flow divergence due to partitioning of melt water into vertical infiltration through moulins and crevasse fields prevalent at lower elevations. Tributary and connector networks between 800 and 1200 m in elevation are correlated with fewer lake occurrences, lower surface velocities (~50 m a−1), and ice flow dominated by internal deformation over basal sliding...
Believe it or not! Massive calving seen at the southern branch of Jakobshavn Isbræ:
The image from scihub reveals that a calving-event has apparently taken place.
A major calving in the middle of Winter! I can't wait to see what happens this Summer.Could it be that this is routine, and that we are just noticing it, or just now have the ability to see it? Helheim had a calving event in early January, and has also retreated substantially over the winter in past years.
Be aware, Helheim is fast moving monster (probably why it is named so), the calving line seen late 2013 moved some 2 - 3 km during the winter, we will follow it during the season to see where it ends this season.
Believe it or not! Massive calving seen at the southern branch of Jakobshavn Isbræ:
Does this Sentinel "PolarView" from the 15th help throw additional light on matters?
The second one, from the 14th, is even less "crystal clear"!
Wow! The massive crevasses were evident earlier but I was thinking they were in a state of suspended animation due to buttressing from frozen mélange in the fjord. I'm going to guess this is an effect of warmer water in Baffin Bay (and so Disko Bay and at the calving front: the mélange is just not strong enough this year to hold back calving.
Were that ice "floating" or it added now to sea level rise?
I don't think the fjord and what is in it, have any effect on the forces coming from Jakobshavn
Were that ice "floating" or it added now to sea level rise?
The ice that was above sea level, more or less, will be added to the current sea level eventually, when melted.
Just to keep you informed, this is the retreat situation since 1851, the years mentioned are the minimums (at least 2013 and 2014)!
Please click on image to enlarge!
Bed elevations were interpolated from a gridded map of radar depth soundings produced by the Center for Remote Sensing of Ice Sheets (CReSIS)(Li, 2009; Van der Veen et al., 2011). Multiple versions of the DEM exist, but based on comparison with other data sets our preferred version is the one located at ftp://data.cresis.ku.edu/data/grids/old_format/2008_Jakobshavn.zip. (http://ftp://data.cresis.ku.edu/data/grids/old_format/2008_Jakobshavn.zip.)The radar data from middle years is carefully reviewed by Gogenini 2014, http://www.igsoc.org:8080/journal/60/223/j14j129.pdf, (http://www.igsoc.org:8080/journal/60/223/j14j129.pdf,) noting the problems arising from terminal roughness, side reflections, and material at the bottom.
The ice thickness is ~850m at the calving front [which converts calving area to calving volume], increases to~1500m, then decreases to ~1200m between 5 and 7km. Beyond this, the ice thickness varies between 1400 and 1200m. We also observe two distinct echoes separated by 100–200m in the along-flow line echogram caused either by side-wall echoes and bed echoes or multiple interfaces at the bed.Oddly, this article does not include the great many subsequent grid overflights with what one supposes are improved radar designs nor provide a bottom line map of the depth profile. Ice thickness would have to be subtracted from surface elevation to get at trough and sill.
Sermeq Kujalleq is bound in a dynamic struggle to stay in contact with the sill at the entrance of the deep trench. It is just a matter of time until this contact will be lost and we might witness a rapid retreat.
Further summer speedup of Jakobshavn subsequently declined in 2013 as the terminus retreated to higher ground. By contrast, the 2009 mean speed was faster than the 2011, despite a more advanced 2009 terminus position. This difference likely reflects the fact that at these time scales, the other processes and feedbacks have a substantial influence on flow.
If the terminus has reached the bottom of an overdeepened region, then the terminus may be able to find a position of transient stability on the high spot farther upstream [located at positions 12 to 17 km in the inset below] as retreat to shallower depths yields slower speeds (Joughin et al., 2012a).
The relatively high surface slope region upstream of the overdeepened basin [1.5º, image below] where the present heights are [80 to 167 m] metres above flotation, may further slow retreat, since it should take more time to thin to near flotation. By contrast, low surface slopes and heights near flotation likely facilitated the rapid retreat since 2009.
While the high spot above the basin may slow flow, the terminus would still be grounded on a bed at least 900 m below sea level, likely yielding speeds well above balance that would maintain strong though potentially diminished thinning. As a consequence, the terminus likely will continue to retreat, albeit perhaps more slowly in the near term, until it again reaches bed depths similar to summer 2012 (1300 m below sea level) at 15 km farther upstream.
At the current stage, further retreat may largely be driven by ice dynamics with only weak coupling to climate forcing. Thus, a re-advance rather than retreat likely would require a period of several years to decades of cooling. Once past the high spot, the trough extends roughly 50 km farther inland at depths below sea level of 1200 m and more before eventually reaching shallower depths.
Thus, although variation in trough width of 3.5 to 5.5 km could modulate the rate of flow, once into this deepest part of the trough, extreme velocities (12 km/yr) are likely to persist as the terminus rapidly retreats. Furthermore, without the [need] to seasonally advance up a relatively steep bed slope as in the past several winters, such high speeds may be sustained year round.
Because the deep trough of Jakobshavn is extremely difficult to measure with conventional techniques, we cannot rule out that some or all of the high spot might be a gridding artifact, in which case retreat may occur even more rapidly. Similarly, we cannot rule out that some bed highs may not have been resolved that could provide additional points of transient stability.
What is the thickness of the glacier at the pinning point [sill] a few km upstream of the calving front? Is it even close to floating?I extracted the flotation graphic from Joughin 2014 and added to #565 above. It is about 150 m too thick, nowhere near floating if we assume the bedrock depth profile is correct. Note the authors themselves are questioning the existence and positions of the sills.
I extracted the flotation graphic from Joughin 2014 and added to 564 above. It is about 150 m too thick, nowhere near floating.
How much of that 628 meter was lost from 2013 to 2014?Not very much, but I wonder if this will be the year that the calving front retreats beyond the sill. Though how would we know if its location and even existence aren't certain? I suppose by a fit to the physics. Yet all is not well there because it seems not to be kicking out any publishable predictions for 2015-20.
The scale on the left for the blue line seems to have been chopped off. Could you indicate the units ?The scale is still there, barely (the m below the 167), it is meters. I do condense the graphic legends to make more room for resolution per the 700 maximal pixel width here. This one had to be radically rescaled vertically in gimp to get its scale readable. The authors did not furnish the underlying numeric data points in journal supplemental (despite utilizing it) so I could not cleanly re-graph it.
relying too the clear bedrock map by SteffenThis older map is an important discovery because it explains a lot of confusion in the journals about where the sill is located, before or beyond the current calving front. Presumably later maps based the 2006-08 experimental radar data are better because those years were the first to reach bedrock.
Including the present calving front unless I am completely wrong? Now the numbers are upside downNice work, sidd and Espen! Not so easy to place the calving front but it looks about right relative to above sea level exposed rock.
Deeply incised submarine glacial valleys beneath the Greenland ice sheet
M Morlighem, E Rignot, J Mouginot, H Seroussi, E Larour
http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html (http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html)
The bed topography beneath the Greenland ice sheet controls the flow of ice and its discharge into the ocean. Outlet glaciers move through a set of narrow valleys whose detailed geometry is poorly known, especially along the southern coasts. As a result, the contribution of the Greenland ice sheet and its glaciers to sea-level change in the coming century is uncertain.
Here, we combine sparse ice-thickness data derived from airborne radar soundings with satellite-derived high-resolution ice motion data through a mass conservation optimization scheme*. We infer ice thickness and bed topography along the entire periphery of the Greenland ice sheet at an unprecedented level of spatial detail and precision. We detect widespread ice-covered valleys that extend significantly deeper below sea level and farther inland than previously thought.
Our findings imply that the outlet glaciers of Greenland, and the ice sheet as a whole, are probably more vulnerable to ocean thermal forcing and peripheral thinning than inferred previously from existing numerical ice-sheet models.
Let's hope sidd has time to pull out a few more of these contour maps for our favorite glaciers!
*M Morlighem
A mass conservation approach for mapping glacier ice thickness.
free full http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf (http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf)
Geophys. Res. Lett. 38, L19503 (2011).
The traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging. While this approach provides continuous maps of ice thickness, it generates products that are not consistent with ice flow dynamics and are impractical for high resolution ice flow simulations.
Here we present a novel approach that combines sparse ice thickness data collected by airborne radar sounding profilers with high resolution swath mapping of ice velocity derived from satellite synthetic-aperture interferometry to obtain a high resolution map of ice thickness that conserves mass and minimizes the departure from observations. We apply this approach to the case of Nioghalvfjerdsfjorden (79North) Glacier.
Let's watch that spelling on Mathieu Morlighem, associated with the Rignot group and now faculty at UC Irvine. The original papers are here:QuoteDeeply incised submarine glacial valleys beneath the Greenland ice sheet
M Morlighem, E Rignot, J Mouginot, H Seroussi, E Larour
http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html (http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html)
The bed topography beneath the Greenland ice sheet controls the flow of ice and its discharge into the ocean. Outlet glaciers move through a set of narrow valleys whose detailed geometry is poorly known, especially along the southern coasts. As a result, the contribution of the Greenland ice sheet and its glaciers to sea-level change in the coming century is uncertain.
Here, we combine sparse ice-thickness data derived from airborne radar soundings with satellite-derived high-resolution ice motion data through a mass conservation optimization scheme*. We infer ice thickness and bed topography along the entire periphery of the Greenland ice sheet at an unprecedented level of spatial detail and precision. We detect widespread ice-covered valleys that extend significantly deeper below sea level and farther inland than previously thought.
Our findings imply that the outlet glaciers of Greenland, and the ice sheet as a whole, are probably more vulnerable to ocean thermal forcing and peripheral thinning than inferred previously from existing numerical ice-sheet models.QuoteLet's hope sidd has time to pull out a few more of these contour maps for our favorite glaciers!
*M Morlighem
A mass conservation approach for mapping glacier ice thickness.
free full http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf (http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf)
Geophys. Res. Lett. 38, L19503 (2011).
The traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging. While this approach provides continuous maps of ice thickness, it generates products that are not consistent with ice flow dynamics and are impractical for high resolution ice flow simulations.
Here we present a novel approach that combines sparse ice thickness data collected by airborne radar sounding profilers with high resolution swath mapping of ice velocity derived from satellite synthetic-aperture interferometry to obtain a high resolution map of ice thickness that conserves mass and minimizes the departure from observations. We apply this approach to the case of Nioghalvfjerdsfjorden (79North) Glacier.
Let's hope sidd has time to pull out a few more of these contour maps for our favorite glaciers!I could sure use Petermann. As with Zach and Niag, there is a real question whether (or how) Morlighem's method takes the upheaval fields into consideration. I would say it doesn't.
I will add Zachariae to that list!
Including the present calving front unless I am completely wrong?
can be contoured with Qgis to arbitrary intervals but the 100m contour already takes hours on a laptopThanks so much for doing this, sidd. Sounds like a high risk operation that has the potential for tying up the computer all day only to wish later different settings had been chosen.
these new maps explains much more than I already knew...Likewise. This is really the 'missing map' for Jakobshavn. Nothing quite like reading a straightened-channel one-slice one dimensional modelling paper while having this map open.
I wanted to ask, does anyone here run a unix ?
Anyone ?
It's an interesting finding.
A cautious response: even if this calving were abnormal, we will likely see an advance in the next weeks that will fill the void. Why?
A.) this glacier flows fast and
B.) now with less flow resistance there will likely be an acceleration making the void filling happen even faster.
Here are annual end of melt season area changes measured by PROMICE.org. These are being updated. I will ask Karina Hansen today to update for 2014 and 2015. We could have that result in a few hours.
name ID lat lon region region ID width 1999/00 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 2012/13
Jakobshavn 14 69.1788 -49.7329 W 105 11.4 -2.75016 -2.4734 -16.357427 -45.617225 -21.235024 -10.015401 -4.155551 -3.829812 -3.202087 -2.174176 -8.725405 -6.69317 -13.742999 -2.825888
In context of the ongoing retreat, I would speculate that this retreat could make further retreat more likely because the acceleration from B.) would cause 'dynamic thinning' that through a positive feedback would reduce glacier bed friction facilitating further thinning and acceleration. This feedback is an amplifier and not runaway but being activated would precondition Jakobshavn glacier for further retreat.
Sorry about the formatting!Nice initiative, Jim. Might want to delete on of the duplicate posts. By 'end of melt season area changes", does he mean retreat of the calving front of Jakobshavn, measure not by a line as we have been doing but by the area in km2 between successive retreat lines? Net area works better for last year when the 2013 vs 2014 advance lines crossed.
Nice initiative, Jim. Might want to delete on of the duplicate posts.
In the attached prepared by Karina Hansen you will see a light yellow polygon illustrating the end of melt season 2014 ice Jakobshavn front position retreated from the Feb 2014 (pink line) and Feb 2015 (green line) positions. The Feb 2014 and Feb 2015 positions are roughly the same with 2014 Feb being further retreated than Feb 2015.
The calving appears to be not abnormal at least in terms of where the front position is and therefore is not a shock but rather illustrates my points A. and B. of this morning's message.
Looking at the distance moved across a transect 5 km upstream of the calving front between 12-28 Feb 15, velocities are moderate by JI standards, averaging 23.1 m/day or 8.4 km/yr but with peak speed of 9.3 km/yr which is quite high for February but seeming below the all-time record set in February of 2013.
This transect corresponds, more or less, to the M9 station in Fig.2 of Joughin 2014 www.the-cryosphere.net/8/209/2014 (http://www.the-cryosphere.net/8/209/2014) below. However a real comparison can only be done by replicating their internal system of measurement which is not feasible.
Not reporting another trivial calving this time, but watch the speed of Jakobshavn over 9 days:
...That is the question I've been looking for an answer to. Assuming the calving face keep retreating at its current rate how long until it gets there?
Is it just too far into the future?
Jakobshavn Issbræ the calving-machine is up in gear again:
The front is much narrower?
The front is much narrower?
It looks that way to me as well. I've taken the liberty of republishing your animations over at:
http://GreatWhiteCon.info/2015/05/jakobshavn-isbrae-calves-yet-again/ (http://GreatWhiteCon.info/2015/05/jakobshavn-isbrae-calves-yet-again/)
I hope that's OK with you? Please let me know ASAP if not.
How do you folks read this image?
S-1 IW HH-polarization on 27.5.2015
Great Espen! BTW your SAR images have very high contrast, have you experimented with taking a logarithm (or alternatively a square root) of the SAR intensity as it is more pleasing to the human eye?
The S-1 SAR-data in the image-files are in amplitude-format, while the "industry-standard" is log_intensity. You can convert amplitude to log-intensity in the following way:
log_intensity = log10(amplitude^2)
This should bring out much more detail for the human eye and you can apply the Photoshop filters afterwards.
I don't know Photoshop but I would imagine there's a plugin that allows for that?The S-1 SAR-data in the image-files are in amplitude-format, while the "industry-standard" is log_intensity. You can convert amplitude to log-intensity in the following way:Have not a clue what you are writing about, is it possible to code in Photoshop?
log_intensity = log10(amplitude^2)
This should bring out much more detail for the human eye and you can apply the Photoshop filters afterwards.
I have some difficulties interpreting the Sentinel images from June 1, maybe Wipneus can help?
I know there were some calving activities lately.
is it possible to get good idea of how thin the ice is there and how long it will take before its gone?
Quoteis it possible to get good idea of how thin the ice is there and how long it will take before its gone?
The thickness ice-to-bedrock for a particular year could be read off a Cresis radar overflight that crossed your area of interest. If there was data for multiple years, that would provide a trend.
However the ice to just north of the main Jakobshavn channel is far from stagnant so it wouldn't be the 'same' ice. The whole ice sheet is sliding downhill so the ice there now will be replaced with ice from the northeast.
Espen ran into that in #630 comparing a late season 28 Sep 2014 to an early season 12 May 14. As the main channel receded past the tongue of the northern icefall, its buttressing was removed and it spilled into the newly opened water.
I looked around for recent ice sheet velocities of this region, finding a Jan 2015 image in a nice Sentinel overview article at http://tinyurl.com/ps7brk8 (http://tinyurl.com/ps7brk8) and another in a May 25 open source article on accurate balance velocites, http://www.geosci-model-dev.net/8/1275/2015/gmd-8-1275-2015.pdf (http://www.geosci-model-dev.net/8/1275/2015/gmd-8-1275-2015.pdf)
Look for the 'big bend' in Jakobshavn to orient yourself. Then note how much of its surroundings to the north are flowing into the system. I posted some speculation earlier about iceshed capture in the future. It would be fairly tricky to demonstrate this over a limited time interval, even ten years, because of differences in satellite sensors.
So JH actually managed to gain ground in the past 12 months.
Do you have a step-by-step protocol for producing interferometric images? I was under the impression that Sentinel-1B (2016 launch) was necessary for this but they somehow produced the Napa earthquake subsidence fringes just from 1-A. (This is not another Radarsat emulation of Sentinel).For InSAR just a repeated orbit is needed, with S-1A that happens every 12 days and with the 2nd unit there's a chance for InSAR every 6 days (provided that the data is acquired).
movement of the ice (in the along-track direction)
Strictly speaking the phase-jump is not an error-term but real signal related to along-track motion (it is caused by the difference in look-angle between individual radar "bursts"). Let's see in the coming years what the InSAR community can wring out of this data.Quotemovement of the ice (in the along-track direction)So the case of Jakobshavn which moves east to west (and slightly down) and a satellite moving almost north to south is quite unfavorable (for error term) because there is almost no component of motion in the along-track direction? Whereas Petermann would be more favorable as it moves south to north and NEGIS is intermediate as it moves diagonally though Zachariae again is west-east.
The purpose of Sentinel 1-B for Greenland would then not be velocity but rather simultaneous 'stereo pairs' that allow construction of precise digital elevation maps (and their change over time)?Radargrammery (stereo pairs) will not work for many reasons including resolution and the repeat-period. However, S-1A&B will be great for ice velocity measurements using coherent and incoherent feature-tracking so there's no need to do interferometry as such. InSAR can be used for more precise measurements (in the across-track direction) in the future provided that the experts figure out how to separate phase caused by along-track ice movement from phase coming from the DEM.
Let's see in the coming years what the InSAR community can wring out of this data.... in the future provided that the experts figure out how to separate phase caused by along-track ice movement from phase coming from the DEM.Seems like they should have figured this out way back in the grant proposal for the satellite series, rather than later on the fly. Maybe. They already had the RadarSat-2 simulation of Sentinel to work with.
The 2014 calving front is the one showing greatest retreat for the date. This might be because the ice stream is advancing faster this year relative to rate of calving in the 'new abnormal' of stationary cold weather.
Seems like there are some advantages from using files from the Sentinel hub itself, notably the ability to manipulate within 16-bits (enlargement, rotation and local contrast), and separate HH and HV polarizations which can also be combined into RGB (blue taken as all 0 or black).
The great downside is that north is not up in Sentinel images nor is a rotational angle provided nor is this angle the same between images. This contrasts with DMI and Landsat. For example the 10 June 15 Sentinel needs an 18.9º rotation.
The HV is brighter in this instance. It seems to better distinguish calved from recently calved from freshly calved. I don't know what the physical basis for this is, maybe calved ice becomes less rough over time. Neither polarization combo is proposing about-to-calf.
The Jakobshavn calving front seems to have moved further into record retreat; that can be measured relative to the last fixed point, the rock island in lower left. If this is July 9th and maximal retreat in 2014 occurred in late Sept, this could get interesting. There are three issues: position relative to basal topography sills and troughs, loss of side buttressing if the calving front should retreat past the 'big bend', and greatly reduced obstruction to side tributary inflow.
The comparison to the Sept 27th maximal retreat of last year is somewhat problematic due to geometric effects in two different instruments, plus there has been more melt-out around our favorite reference rock late season adding to the alignment/rescaling uncertainty. Still, after moving Espen's calving front line over to this year's image shows there has been a modest level record retreat.
The June 10th has come in ... this one is rotated CW to better match true north and DMI. This has the effect of rotating the calving line around the reference rock.
S1A_EW_GRDM_1SDH_20150710T095917_20150710T100017_006747_0090B2_65F1
Water pressure is essential for basal crevasse penetration, but it may also be significant in surface crevasses. The process of hydrofracturing by water in surface crevasses is believed to have been a critical factor in the collapse of the Larsen B Ice Shelf. However, while water in surface crevasses may be important, it is extremely difficult to quantify. The relationship between surface melt rate and crevasse water depth depends on the distribution, shape and depth of crevasses, and melting and refreezing on crevasse walls, as well as potential drainage of water from crevasses into englacial, subglacial or proglacial water bodies. As such, it is currently impossible to estimate even an order of magnitude for crevasse water depth at Store in summer. However, outside the 3-month summer melt sea-
son, surface crevasses must be assumed to be dry. http://www.the-cryosphere.net/8/2353/2014/tc-8-2353-2014.pdf (http://www.the-cryosphere.net/8/2353/2014/tc-8-2353-2014.pdf)
giant blue whale
... welcome to use any drills from my toolbox for that project
I would suspect that exposure to seawater would contaminate and parts per million / billion variations what I've cores try to measure...
Maybe we could get a cheap ice core by scraping a tool along one of these beasts longitudinally after it has shoaled at the far west end of the fjord (Espen?). Till at the very bottom would be especially informative. Its age could not be dated by layer stratigraphy because that is long gone but its thickness, minerals and certain isotopes like beryllium could be informative.
exposure to seawater would contaminate and parts per million / billion variations what ice cores try to measure..Surprisingly, small molecules, ions and tephra don't diffuse notably in a cold high pressure ice Ih lattice. If they did, after 100,000 years, there would not be storm-level resolution in a 1 mm annual layer. (See http://onlinelibrary.wiley.com/doi/10.1002/jqs.2684/full (http://onlinelibrary.wiley.com/doi/10.1002/jqs.2684/full))
I wonder if that north face of the south branch could develop further, or if it's a dead end.
btw, the gif shows 2014 by error for the July dates.
I wonder if that north face of the south branch could develop further, or if it's a dead end.
btw, the gif shows 2014 by error for the July dates.
I usually only lurk, as I have no expertise in this subject whatsoever, but I was intrigued by Espen's animation above. There seem to be 3 largish rocks that appear to the left of the North branch in the 2015 frames which don't show on the 2014 picture. Is this indicative of rapid thinning of the glacier at this point, or is there a more likely explanation?
Much of the north face is grounded below sea level and the below sea level grounded portion goes fairly far inland.
I absolutely guarantee the north face is going to surprise us.
Looking at the north face in the most recent calving video, I'm struck by how tall it is. I can hardly imagine that this 3rd branch will be able to retreat very quickly through such a mountain of ice, after all, despite this area being grounded below sea level, it is quite shallow. There is also a second "cape ice" in the making which probably will result in two separate bulges in the north face, rather than one long calving front which could perhaps be somewhat unpredictable. Then again, I guess my inability to see where a surprise is supposed to come from, is also the reason I will be surprised :D.
uhm, I am not sure if I have my maths right, but the taller a glacier cliff is, the more prone it is to cliff failure and cliff+hydrofracturing. So I do not see how one should connect a tall cliff to stability. It is a main driver of dynamic behaviour...
Still moving on, very close at record retreat for Jakobshavn:
It's as if the glacier saw that red line you drew on the previous post.If it doesn't break out this season, we'll need to seriously revisit the 'stuck on the exit ramp' scenario a few posts back. #717.
what the latest animation is showing. water nearest the north face of the southern branch filled with melange
The animation below shows an illustrative scenario in which the calving front rattles around in a potential well midway up the ramp that it can't climb out of. Every time it tries (calving faster), that releases the glacier to come forward faster, and vice versa. The diagram is strictly heuristic (or if you prefer, speculative rubbish) but not physically unmotivated (early Joughin papers). We're more familiar with received wisdom that glacier retreat accelerates once it is past a sill, this is more of the same.
So what would it take to get the little ball up over the hump? the calving would have to increase faster than the downhill movement until a break-even point where there isn't enough mass between the calving front and the sill crest to maintain velocity.
any buttressing effect between the north side and the main glacier? If so, then its receding could help the calving front retreat further.Yes, depending on the thickness and velocity (~ momentum) of the ice coming roughly orthogonally off the north side, the effect would be to compress the main ice stream to its walls and surface rocks on other side, tending to inhibit motion and calving. The main north branch at one time played this role as did a pinning point mid-fjord. The large bend upstream would have a similar effect. Whether these add up to anything quantitatively is questionable. Really it is the north side that has become uncorked.
Optical and SAR can be compared/merged once they are projected to the same map projection.
September 28 2014 is still ahead in an important km long region in the southern branch!Maybe get back to us on this in a week or so? I am recalling 2014 waxing and waning through the summer (not proceeding steadily to Sept climax which it might not have been since it was so cloudy. You can see it was about to shed big chunks.
Whoa ... this looks to be the biggest calving ever. Just at DMI resolution though ... need to chase down original Sentinel.
some heavy calvings line just behind the present calving frontYes, most odd. Landsat from yesterday does not have this yet.
Quotesome heavy calvings line just behind the present calving frontYes, most odd
Quotesome heavy calvings line just behind the present calving frontYes, most odd
The gif Espen posted above seems to suggest advancement of glacier not retreat. Could 1 Aug image be taken just at start of calving event?
No, the DMI image is from today's Sentinel too.
However we have a number of rogue individuals posting on these forums.
Looking on Modis between 1/8 and 30/7 I could not detect any differences, so I was tempted to think that whatever happened was after the Modis 1/8 pass but could of course be wrong.
If right, and a calving event takes some time (I think an hour was mentioned on thin ice video), and the latest sentinel image is after the 1/8 Modis pass then catching the calving event in progress doesn't seem impossible, though the image would have to be fairly early in the calving process.
Perhaps too many conditional 'and's in that.
OK if it is backing off of the under ice ridge then are we back to tabular calving?Quotesome heavy calvings line just behind the present calving frontYes, most odd. Landsat from yesterday does not have this yet.
if it is backing off of the under ice ridge then are we back to tabular calving?No, Jakobshavn is done with tabular calving (unless you count breakup of seasonal melange that builds during the winter).
can offer some help during August...once the processing graph is set up it's rather simple to process new acquisitions...That would be fantastic if you could walk us through an example with a Jakobshavn file. We (me that is) definitely need to move on to the next level of processing using this Toolbox.
What I'm looking at is this. Sea water is denser than fresh water. As you cool sea water with ice you also reduce its salinity. What wins cooler denser sea water or less dense melt diluted sea water?Quoteif it is backing off of the under ice ridge then are we back to tabular calving?No, Jakobshavn is done with tabular calving (unless you count breakup of seasonal melange that builds during the winter).
What I expect to see as Jakobshavn retreats farther out of its fjord back into the narrower winding south channel is reduced heat exchange between warm ocean water and ice at the grounding line because the attack surface is less accessible and the water will have been cooled. However the interface is taller to the extend the ice stream is retreating over a reverse grade (ie down from a sill into a trough).
There will still be plenty of convection (heat transfer by mass transport away) via churning induced by frontal calving and upwelling buoyant meltwater, but the resulting ocean water the glacier faces is then colder than open ocean water because circulation and mixing are reduced in the narrow channel and dominated by ice. (Picture the ice stream 10, 20, or 30 km further inland and the long cul de sac of ocean water.)
The icebergs we see streaming away must be balanced by return flow of deeper waters. However surface transport is fairly shallow (tens of meters) whereas the distance through water to bedrock approaches 1500 m. Thus if this were the only consideration, retreat would slow. The narrowness of the channel could offset this somewhat through turbulent interactions with the wlls.
Jason Box just posted an excellent popular piece on the other considerations which almost all favor faster retreatL
http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html (http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html)
Happy to help, could you start a topic in the Developers' Corner and I'll jump in? Basically it would be good if you described what are the characteristics of the end product you want (projection etc.).Quotecan offer some help during August...once the processing graph is set up it's rather simple to process new acquisitions...That would be fantastic if you could walk us through an example with a Jakobshavn file. We (me that is) definitely need to move on to the next level of processing using this Toolbox.
Happy to help, could you start a topic in the Developers' Corner and I'll jump in?Great, most helpful. Let's just use the Sentinel-2 one already started so as not to spread this out all over. I would say, how do we process a Sentinel image so that it co-registers with Landsat images of Greenland which are in local Mercator projection.
Sentinel-1 imagery is provided in satellite geometry which is slightly different depending on the type of Level 1 product. For the detected GRD products, the imagery is provided in ground range, x, and azimuth, y, geometry whereas for complex SLC products, the imagery is provided in slant range, x, and azimuth, y, geometry.
This is described at https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/product-types-processing-levels/level-1. (https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/product-types-processing-levels/level-1.) As both GRD and SLC imagery are provided in satellite geometry, its orientation with respect to true north will vary with latitude and incidence angle. Thus it is not possible to accurately orientate the imagery with respect to north using a single rotation as this depends on both the x (range) and y (azimuth) position within the image. [[This could be provided by a simple grayscale mask but isn't.]]
Although Sentinel-1 imagery is not provided in a geocoded orientation (like your Landsat image), the product annotation gives a complete description of the transformation from pixel coordinates (x,y) to latitude & longitude via the geo-location data set record.
This data set is described in the Sentinel-1 Product Specification document S1-RS-MDA-52-7441 available from https://sentinel.esa.int/documents/247904/349449/Sentinel-1+Product+Specification+3.0. (https://sentinel.esa.int/documents/247904/349449/Sentinel-1+Product+Specification+3.0.) In particular see Section 6.3.1.7 for a description of the geolocation grid. Below is an example of first point within a grid from a GRD product:
<geolocationGrid>
<geolocationGridPointList count="483">
<geolocationGridPoint>
<azimuthTime>2015-08-04T22:03:55.263139</azimuthTime>
<slantRangeTime>4.976224778237438e-03</slantRangeTime>
<line>0</line>
<pixel>0</pixel>
<latitude>7.768200950286953e+01</latitude>
<longitude>-9.014424336694947e+01</longitude>
<height>-2.077938625589013e-01</height>
<incidenceAngle>1.937838349149362e+01</incidenceAngle>
<elevationAngle>1.737100868906543e+01</elevationAngle>
</geolocationGridPoint>
Note that an approximate orientation of the image with respect to north can be found by extracting the platformHeading parameter within the product annotation (see Table 6-31 of the above product specification document). Note that this is the orientation of the satellite and not the image. An example of this parameter is given for an image at a high latitude:
<generalAnnotation>
<productInformation>
<pass>Ascending</pass>
<timelinessCategory>Fast-24h</timelinessCategory>
<platformHeading>-4.390998067621028e+01</platformHeading>
Image rotated by 15º gives quite a good local fit (to Landsat) using that lake in the lower left and the ice fall dividing north and south branches. Looks like a very large piece has calved or is about to.
https://www.google.com/maps/place/Bosphorus,+Turkey/@41.1194435,29.075278,2200m/data= (https://www.google.com/maps/place/Bosphorus,+Turkey/@41.1194435,29.075278,2200m/data=)!3m2!1e3!4b1!4m2!3m1!1s0x14cacaf6a1b454cf:0x7bab8b9dc19261dcQuoteif it is backing off of the under ice ridge then are we back to tabular calving?No, Jakobshavn is done with tabular calving (unless you count breakup of seasonal melange that builds during the winter).
What I expect to see as Jakobshavn retreats farther out of its fjord back into the narrower winding south channel is reduced heat exchange between warm ocean water and ice at the grounding line because the attack surface is less accessible and the water will have been cooled. However the interface is taller to the extend the ice stream is retreating over a reverse grade (ie down from a sill into a trough).
There will still be plenty of convection (heat transfer by mass transport away) via churning induced by frontal calving and upwelling buoyant meltwater, but the resulting ocean water the glacier faces is then colder than open ocean water because circulation and mixing are reduced in the narrow channel and dominated by ice. (Picture the ice stream 10, 20, or 30 km further inland and the long cul de sac of ocean water.)
The icebergs we see streaming away must be balanced by return flow of deeper waters. However surface transport is fairly shallow (tens of meters) whereas the distance through water to bedrock approaches 1500 m. Thus if this were the only consideration, retreat would slow. The narrowness of the channel could offset this somewhat through turbulent interactions with the wlls.
Jason Box just posted an excellent popular piece on the other considerations which almost all favor faster retreatL
http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html (http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html)
The transient summer speeds we observe for 2012 (>17000myr−1) appear to represent the fastest observed speed for any outlet glacier or ice stream in Greenland or Antarctica. This yields a speed up by more than a factor of four relative to the 1990s, while the mean annual speedup is by just under a factor of 3. If, as the glacier recedes up the trough, it is able to maintain the peak speeds year round, then a sustained speedup by a factor of 4 of 5 is conceivable based on recent behavior, which is about half of the ad hoc tenfold upper limit on speed proposed by Pfeffer et al. (2008). Nevertheless, these speeds would occur in a trough roughly twice as deep as prior to the speedup.
Hence, a tenfold increase in ice flux may be possible for Jakobshavn Isbræ if the trough does not narrow substantially with distance upstream. Equivalently, while the increase in terminus speed and the glaciers overall maximum speed may remain under a factor of five, as the terminus retreats farther inland where the speeds now are comparatively slow, the relative speedup is much greater (e.g., if the terminus retreated to M26 with a speed of 16000myr−1, this would represent a twelve-fold speedup). Thinning by hundreds of meters to a terminus near flotation, however, yields something closer to a ten-fold flux increase. It is unlikely that such retreat could be sustained for more than a few decades because the terminus would rapidly retreat ∼ 50 km to shallower depths (Joughin et al., 2012).
Quite bizarre.Attached is a cut-out of the original DMI posting (inset) and a 2x bilinear enlargement. I cannot see the letters myself but your interpretation of an extensive watermark ruining the image makes sense.
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This project represents a unique collaboration between government and industry. MacDonald, Dettwiler and Associates Ltd. (MDA) will own and operate the satellite and ground segment. The Canadian Space Agency (CSA) helps fund the construction and launch of the satellite and will recover this investment through the supply of RADARSAT-2 data to the Government of Canada during the lifetime of the mission.
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Nice shot, if you zoom into "cap ice" there seems to be a promontory /embayment forming on it's southern shore just past the cornerI'm thinking you mean the area indicated with the white arrows below. That would be quite interesting to track over the season and indeed the three Landsat-8 years we have now. It may be a new development enabled by buttressing withdrawal of the main ice stream.
What I still don't get about Jakobshavn is why there is so little interest in the areas east of the currently active main channel... how future contributions to SLR if something like 90% (probably more) of its drainage is ignored? Have they given up because the main channel more or less inaccessible?From watching AGU meeting abstracts and posters from Ph.D dissertations that never seem to emerge as journal articles, I'd guess quite a few approaches haven't panned out.
Further summer speedup of Jakobshavn Isbræ
I. Joughin and B. E. Smith
http://www.the-cryosphere-discuss.net/7/5461/2013/ (http://www.the-cryosphere-discuss.net/7/5461/2013/)QuoteThe transient summer speeds we observe for 2012 (>17000myr−1) appear to represent the fastest observed speed for any outlet glacier or ice stream in Greenland or Antarctica. This yields a speed up by more than a factor of four relative to the 1990s, while the mean annual speedup is by just under a factor of 3. If, as the glacier recedes up the trough, it is able to maintain the peak speeds year round, then a sustained speedup by a factor of 4 of 5 is conceivable based on recent behavior, which is about half of the ad hoc tenfold upper limit on speed proposed by Pfeffer et al. (2008). Nevertheless, these speeds would occur in a trough roughly twice as deep as prior to the speedup.
Hence, a tenfold increase in ice flux may be possible for Jakobshavn Isbræ if the trough does not narrow substantially with distance upstream. Equivalently, while the increase in terminus speed and the glaciers overall maximum speed may remain under a factor of five, as the terminus retreats farther inland where the speeds now are comparatively slow, the relative speedup is much greater (e.g., if the terminus retreated to M26 with a speed of 16000myr−1, this would represent a twelve-fold speedup). Thinning by hundreds of meters to a terminus near flotation, however, yields something closer to a ten-fold flux increase. It is unlikely that such retreat could be sustained for more than a few decades because the terminus would rapidly retreat ∼ 50 km to shallower depths (Joughin et al., 2012).
60 km upstream there is a three way split in the main channel. Jakobshovn is flowing the shallowest narrowest channel.It's one thing to locate this area on the bed topography, ice thickness, surface elevation maps ... another to co-locate it accurately on surface velocity, Landsat and Sentinel maps. I've posted extensively on the confluence area before ...
Melting all ice below 2000 m (and nothing about it) will create (impossible) floating ice mountainsNot talking about that. Find the 2000 m contour. Dig a trench straight down to bedrock with your backhoe. Now measure the ice volume downhill. Then measure the ice volume uphill. Divide. Get small number (?)
Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011.
We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available.
Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change.
However, there are problems with this approach, most notably; the pure colors (red, yellow, cyan and blue in this instance) merged with and were eaten by their less pure neighbours so to speak. This effect becomes particularly visible at low elevations where the slope is steeper and the different colors are crammed tighter together. Then, for some reason (I'm tempted to say god knows why, but I'm not sure he does this time) there turns out to be 36 different contours, for one 32 would have fitted perfectly into their color system, as opposed to the current solution which tries to divide 256 on 9, but more importantly it would allow each contour to represent a leap of exactly 100 meters, as opposed to 88,1m which I got from pixel counting their color scale (which by the way measures 241, a prime). Is this because 88 meter fits some margin of error or something like that, or do they just want to mess up the diagrams of excel noobies like me?
Click to enlarge.
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?
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).
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.Thank you A team for the lovely reference on ice thickness etc.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.
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?
seems Jakobshavn did something very serious, bet this one is one of the top 3 within the last 5 years.Excellent spotting.
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.
have a look at the sequence of 17. 18. 19 July 2015 isn't that a lunar month earlier?Yes, there's a shallower zone at the mouth of the fjord where the large icebergs get stuck for awhile.
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 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
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?
2at 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.
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!
It's amazing also how much more exposed rock there is.
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.)
...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!)
None of this ice was floating so it all goes to sea level rise: 8.83 * 2.78 = 24.5 microns
...
The calculation assumes full melt-out (which won't take long in Baffin Bay in August).
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 animation compares the region east of the calving front for the 14 and 16th August Landsats. The latter has thin clouds over some of the image. The alignment is anchored in the upper left via a rotation by a rotation of 5.63º and is not globally ideal. It will need a click to get rolling.
The lower three images look at the Radarsat for changes that took place on the 17th. There does seem to have been further calving lobes in the south.
The animation compares the region east of the calving front for the 14 and 16th August Landsats. The latter has thin clouds over some of the image. The alignment is anchored in the upper left via a rotation by a rotation of 5.63º and is not globally ideal. It will need a click to get rolling.
The lower three images look at the Radarsat for changes that took place on the 17th. There does seem to have been further calving lobes in the south.
From this superb animation it almost seems like there is another northern branch developing on north wall of the south (main) branch. To my untrained eye it suddenly looks more than just random side calvings and general widening of the channel, but rather like a defined inroad deeper into the cliff.
This is what cliff collapse looks like on a 5km wide, 1Km plus deep grounded front, Bassis in action, together with hydro crevassing and fast flow. I shudder to think whats Thwaites will look like over a 55 Km front and no sideways buttress.
This is what cliff collapse looks like on a 5km wide, 1Km plus deep grounded front, Bassis in action, together with hydro crevassing and fast flow. I shudder to think whats Thwaites will look like over a 55 Km front and no sideways buttress.
You're not the only one.
What amazes me the most, is the total lack of interest from my countrymen.
A-team, marvellous images above.
(Small potatoes.)The animation compares the region east of the calving front for the 14 and 16th August Landsats. The latter has thin clouds over some of the image. The alignment is anchored in the upper left via a rotation by a rotation of 5.63º and is not globally ideal. It will need a click to get rolling.
The lower three images look at the Radarsat for changes that took place on the 17th. There does seem to have been further calving lobes in the south.
From this superb animation it almost seems like there is another northern branch developing on north wall of the south (main) branch. To my untrained eye it suddenly looks more than just random side calvings and general widening of the channel, but rather like a defined inroad deeper into the cliff.
Most, if not all, of that north wall of the south branch is grounded below sea level. The portion of the ice sheet that is grounded below sea level goes well into the interior. That is a new calving front that will eventually dwarf the north calving front.
A bathymetry survey of northwest Greenland took place July 22-August 19 and Sept 2-Sept 14 from Ilulissat to Thule. We deployed a multibeam Reson 7160 with 512 beams installed on the hull of the Cape Race vessel, with enhanced capabilities for fjord wall and ice face mapping. The survey tracks were optimized with airborne gravity data collected by NASA Operation IceBridge which indicated the presence of troughs, bed topography mapped inland using a mass conservation approach, and the spatial distribution of ice discharge.
The goal was to identify all troughs that are major pathways for subsurface ocean heat and constrain glacier ice front thickness. The data reveal many deep, U-shaped, submarine valleys connected to the glaciers, intercut with sills and over deepened in narrower passages where former glaciers and ice streams merged into larger units; as well as fjords ending in shallow plateaus with glaciers in retreated positions.
The presence of warm, salty water of Atlantic origin (AW) in the fjords is documented using CTD. Some glaciers sit on shallow plateaus in cold, fresh polar waters at the end of deep fjords, while others are deeper and standing in AW. Satellite imagery from 1962 to 2015 illustrate how the evolution of the glaciers under ocean thermal forcing has been modulated by the presence and/or absence of natural pathways for AW.
IRIS established the Greenland Ice Sheet Monitoring Network (GLISN) of seismic and geodetic sensors to observe the dynamic behavior of the Greenland Ice Sheet as it interacts with the atmosphere, oceans, and solid Earth. GLISN offers the unique ability to record, understand, and respond to changes in the size and scope of the Greenland Ice Sheet’s behavior as it reacts to climate change. Glacial-earthquakes are increasing in occurrence, and their spatiotemporal patterns continue to evolve. Rates of crustal seismicity are also expected to grow as ice melts and withdraws, but the background rates are poorly known.Here is what we are looking for (legend for first image):
Models of the Greenland Ice Sheet are hampered by limited knowledge of its basal conditions including the geothermal heat flux, and characterization and interpretation of mass-loss signals observed using GRACE and GPS data are complicated by limited knowledge of the viscoelastic properties of the crust and mantle underlying Greenland.
Seismic imaging techniques using observations of the propagating seismic wavefield can characterize the subsurface structure, permitting inference of heat flux and the space- and time-varying response to surface loading and unloading. Similarly, analyses of seismic source signals due to ice and water motion, rock fracturing, and ocean loading provide constraints on processes including iceberg calving, deformation within the ice mass and at the bed, changes in the bedrock stress state, and variability in sea state and sea-ice cover. Such observations provide key input for the effort to understand the effects of surface melt and ice-ocean interactions on ice-sheet and glacier dynamics.
All data and metadata are freely and openly available through the IRIS Data Management Center. GLISN allows the Arctic science community full access to year-round recordings of seismic and geodetic signals produced by the Greenland Ice Sheet.
Spectrogram (bottom) and waveforms (top) of of 14 s of seismic data showing one intermediate depth (marked with red box) and three shallow icequakes (Röösli et al., 2012). Spectrum of the intermediate depth icequake is characterized by high frequency content in the 20-80 Hz range; shallow icequakes are characterized by much lower frequency content in the 10-20 Hz range. Waveforms at the top are bandpass filtered in the 1-80 Hz range.Here is one of a dozen or so seismic studies in West Greenland:
Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland
JM Amundson et al
http://onlinelibrary.wiley.com/doi/10.1029/2008GL035281/full (http://onlinelibrary.wiley.com/doi/10.1029/2008GL035281/full)
The recent loss of Jakobshavn Isbræ's extensive floating ice tongue has been accompanied by a change in near terminus behavior. Calving currently occurs primarily in summer from a grounded terminus, involves the detachment and overturning of several icebergs within 30–60 min, and produces long-lasting and far-reaching ocean waves and seismic signals, including “glacial earthquakes”. Calving also increases near-terminus glacier velocities by ∼3% but does not cause episodic rapid glacier slip, thereby contradicting the originally proposed glacial earthquake mechanism. We propose that the earthquakes are instead caused by icebergs scraping the fjord bottom during calving. The recent loss of Jakobshavn Isbræ's extensive floating ice tongue produces long-lasting and far-reaching ocean waves and seismic signals
LamentingIt looks to me from that June 2015 phone-filming of a large calving event that much of the front is no longer visible from the last rocks on the SE side of the south channel. That would be ever so much more the case so today -- the calving lobe is around the corner. It would be very dangerous to go out on the adjacent crevasse fields, even slow moving ones. Still, the noise and bergs floating by would be impressive even if the primary calving was not visible or several km away.
The best vantage point really is the divider between north and south branches. While this looks like a crazy unstable icefall, several years of Landsat show that it is very stable. It would take a helicopter to get there and, if Greenland is anything like Mexico, you would not want to pay the return fare in advance.
those crevasses aren't harmless... to scout a location in advanceFine, stay home then and read the adventure blog. WorldView for 25 Aug 2012 below.
Neven, did you change your name from Akropolis to Curlin (as the WP-article calls you)?
There's a great article (http://www.washingtonpost.com/news/energy-environment/wp/2015/08/19/one-of-the-worlds-fastest-melting-glaciers-may-have-just-lost-its-biggest-chunk-of-ice-ever/) up on the Washington Post website linking to the ASIB blog post on this, with reactions from Alley, Box and Rignot.
2. How big is a calving, and how long a break before a new calving is starting?
3. Why on earth dont they pool part of their respective budgets to fund some serious surveillance equipment up there?
Fine, stay home then and read the adventure blog. WorldView for 25 Aug 2012 below.
1. Typical scientist reaction from one corner.Really. Staking out the middle ground, not go a micron beyond the data? Box, Rignot, Hansen have a better idea -- it's past time to get the message out and stop the equivocating blather.
monitor the calving front year round from space, now that S-1 IW every 12 days is virtually guaranteed.., even more often with the 2nd satelliteYes, the Sentinel program is a huge step forward in terms of really systematic year round monitoring of Jakobshavn. At Petermann, 81ºN, there can be 3-4x daily coverage by Landsat, Sentinel, Modis and NOAA. However available daylight limits non-radar satellites to day 33-268 and in summer clouds can be present for weeks on end. Oddly coverage at Zachariae/Niog at 79ºN is far less frequent.
Didn't Schoof or someone have a Glen's law exponent of 4 way back in 2007?sidd, I edited cites and verbiage from all the AGU abstracts; these provide more Glen flow history. It takes a very specialized type of laboratory to make physically relevant experimental measurements. The 'n' is discussed fairly frequently, the poorly characterized 'A' and its temperature dependence are usually passed over. The sensitivity of model outcomes to their variation is occasionally explored.
that white line sticking out of the latest image of the south branch -- it's just a contrail, isn't it?Good suggestion. The white line can also be seen in the second image though it's less noticeable (dissipated?). It seems out of kilter with other cloud forms in the image. We've also seen elongated smoke plumes at this latitude. Given the low resolution of these images, further analysis seems infeasible.
image comparison slider tool is so effective.Most be stock code, I see it on other sites so wonder if WordPress could support it. In fact one of the bloggers here had it going on a personal site, am recalling artische penguin. I'm skeptical though that it is as transportable as an animated gif. It may just be an active alpha transparency channel over a two image stack.
rapid undercutting of a full face by warmer waterThat'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.
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/ (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 (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.
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.
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)!
anyone measuring total JH flux....all sorts of ice crumbling into the much-longer fjord from newly-exposed cliffBriefly, I am headed out on a camping trip and will be offline for a few weeks.
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?
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 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.
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.
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.
-- this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.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):
-- that is what they are getting paid for? And that is what the whole circus is all about, but we're normally quicker!
"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?
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.
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.
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.
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".
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:
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.I find it amazing that the iceberg C moved 18.5km in 12 days, which is some 1.5km per day. There must be a strong current that side of the fjord pushing the iceberg outward so quickly.