Arctic Sea Ice : Forum

Cryosphere => Antarctica => Topic started by: Yuha on July 09, 2013, 09:50:07 PM

Title: PIG has calved
Post by: Yuha on July 09, 2013, 09:50:07 PM
The long awaited calving has apparently happened:

http://www.bbc.co.uk/news/science-environment-23249909 (http://www.bbc.co.uk/news/science-environment-23249909)
http://www.awi.de/en/news/press_releases/detail/item/huge_iceberg_breaks_away_from_the_pine_island_glacier_in_the_antarctic/?cHash=2e9c4e2ca33a2385bf8e8f881c41b0ca (http://www.awi.de/en/news/press_releases/detail/item/huge_iceberg_breaks_away_from_the_pine_island_glacier_in_the_antarctic/?cHash=2e9c4e2ca33a2385bf8e8f881c41b0ca)
Title: Re: PIG has calved
Post by: AbruptSLR on July 09, 2013, 11:58:23 PM
Yuha,

That is a very timely post and proves that ice shelves can calve even during the dead of an Austral Winter.  We will just have to see how fast things accelerate in the Antarctic.

Best,
ASLR
Title: Re: PIG has calved
Post by: Anne on July 10, 2013, 01:31:35 AM
Yuha,

That is a very timely post and proves that ice shelves can calve even during the dead of an Austral Winter.  We will just have to see how fast things accelerate in the Antarctic.

Best,
ASLR
ASLR, can you please elaborate on this:
What should not be a surprise, [Prof Humbert] says, is that it has occurred in deep winter when the ocean is covered in sea-ice. This relatively thin covering would always be overwhelmed by the internal stresses in the massive ice shelf.
That comment doesn't explain to me why the calving has happened now, because I don't know the basic assumptions she's making. What impels the glacier and on what sort of bed is it moving?
Wikipedia (http://en.wikipedia.org/wiki/Pine_Island_Glacier) is interesting for people like me at PIG 101, but seems to cast no light on why winter calving is not a surprise. Can you help out ?

And what are the questions behind this?
What will be interesting now, she [Prof Humbert] adds, is to see how long it takes for the berg to move out of the bay in front of it. It could take several months. TerraSAR-X will provide the tell-tale data.

With many thanks for your assiduous illumination on all matters Antarctic.
Title: Re: PIG has calved
Post by: AbruptSLR on July 10, 2013, 05:19:03 AM
Anne,

Thank you for you astute questions, and while I may be assiduous, I am more of a student rather than an illuminator, of all matters Antarctic, but I will give the best responses that I can:

- First, I stated that Yuha's post was timely, because I believe that the warm CDW entering the PIG trough is actually protected by the presence of the sea ice; and the timing of the calving both confirms this (in my mind).  Most researchers expect the rate of retreat of the PIG grounding line, GL, to slow as the GL approaches rougher bed conditions; however, if the buttressing action of the Pine Island Ice Shelf, PIIS, (part of which just calved) degrades fast enough, and if the advection of sufficiently warm CDW is strong enough then the GL will continue past the rough terrain that it is approaching.
- Second, I believe that the calving could have happened any time, but that it happened now because the advection of warm CDW cause: (a) sufficient basal ice melt of the local PIIS connecting to shore to weaken it so that; (b) hydrodynamic drag forces from the exiting current and tides, and internal ice stresses (thermal, flexural and shear) to exceed the crack propagation strength (and shear strength) of the local portion of the PIIS connection to the shore.  You should realize that the PIIS is floating (except where it connects to the shore on one or typically both sides of the PIG trough).  The grounded glacier is several kilometers upstream and thus while it continues to slide forward over bedrock and glacial till, its actions has little to do with the calving.  Also, note that the velocity of the ice shelf is faster than the glacier's ice velocity, thus contributing to the thinning of the ice shelf from the GL out toward the face of the ice shelf.  Let me know if you want more details on why the thin outer portion of the ice shelf calves when its internal strength (which weakens as it thins and warms from the CDW) is exceeded by the internal stresses on the ice shelf (significantly associated with the shear restraints from the shores while the center portion of the ice shelf is moving outward faster then the edges).
- Regarding the movement of the berg out of the bay, this is dependent on many factors, including: (a) the strength and directions of the currents (including advection from the salinity gradient of salty water flowing into the lower portion of the trough and fresher water flowing outward at the upper portion of the trough), eddies and tides; (b) storm-action, storm surge, winds and barometric pressure changes; (c) the presence and strength of adjoining sea ice; and (d) the nature of the grounding risks for the berg.  If the berg does not clear the bay, then it may be possible for the PIIS to advance sufficiently to run into the grounded berg; which might temporarily slow the velocity of the ice shelf until the berg became un-grounded; but it is most likely that the berg will float out of the bay during the Austral Spring sea ice break-up.

You should also note that the Thwaites Ice Tongue surged in Sept. of 2012 (when there was still a lot of adjoining sea ice); and you may want to review some of my earlier posts in the "Surge" thread.

I hope that some of this is helpful.  In any event it is a fascinating phenomenon to observe.

Best,
ASLR
Title: Re: PIG has calved
Post by: Anne on July 10, 2013, 10:49:21 AM
ASLR,

Thank you for your patience. Much to think about here.
Title: Re: PIG has calved
Post by: AbruptSLR on July 10, 2013, 03:14:14 PM
Anne,

You can think of the glacial ice as thick honey that flows and thins under the influence of gravity, and when it is thin enough then it floats on top of the ocean water.

Another aspect of this calving event that I did not previously mention is that the crevesse occurred significantly further upstream than experts had previously estimated (resulting in a larger berg); which to me implies that the influence (both basal drag and melting) of the advection of warm CDW is more important than what those experts had previously thought; which further implies that the PIIS may break-up faster than such experts have previously estimated.

Best,
ASLR
Title: Re: PIG has calved
Post by: Lynn Shwadchuck on July 10, 2013, 03:29:46 PM
Thanks, Yuha, for posting this. The BBC story is careful to say these calving events occur naturally without climate change but the warm water underneath is speeding things up. The 6-step photos they've posted are great for those of us who don't diligently stay on top of images.
Title: Re: PIG has calved
Post by: Peter Ellis on July 12, 2013, 06:22:51 PM
url=http://en.wikipedia.org/wiki/Pine_Island_Glacier]Wikipedia[/url] is interesting for people like me at PIG 101, but seems to cast no light on why winter calving is not a surprise. Can you help out ?

You're overthinking it.  A common misconception is that glaciers only calve in the summer when they warm up, and that in the winter they're held in place by the frozen sea ice all around them.  The professor's just explaining that this is rubbish, and that the PIG could have calved at any time, including winter.  Sea ice is a thin skim on the surface and cannot hold back the calving event, just like you can't use Pringles as bookends.
Title: Re: PIG has calved
Post by: Anne on July 15, 2013, 02:37:55 AM
Thanks. Makes sense. I get that glaciers move all the time but don't begin to understand what makes them move. Is it really all down to gravity?
Title: Re: PIG has calved
Post by: AbruptSLR on July 15, 2013, 03:31:22 AM
Anne,

While there are a large number of factors that control the rate and volume of glacier ice movement; the only driving force is gravity.

Best,
ASLR
Title: Re: PIG has calved
Post by: sidd on July 15, 2013, 05:04:55 AM
Gravity drives, but thermo will not be ignored. After all glacier is fed in accumulation zone through tremendous release and absorption of solar driven latent heat.

For PIG (and others) the ice actually moves by refluxing as well as flow. It melts in the cavity at grounding line from hot CDW influx, the fresh water release goes up as fast as it can along the bottom of ice shelf and _refreezes_ near the seaward edge, so the ice near that edge is actually thicker than further upstream. Then, as we see, the seaward chunk breaks off, and we run the movie again.

This refluxing happens beneath glaciers also.

One of these days in my copious spare time, I shall have to work out the relative magnitudes of flow vs reflux in mass transport. More likely, someone will point out that the calculation has already been done and point me to a reference. I suspect that streamflow is more important, but i dunno yet.

sidd
Title: Re: PIG has calved
Post by: AbruptSLR on July 15, 2013, 04:54:20 PM
Anne,

As Sidd points out, my simplistic response may not be addressing the heart of your confusion.  His additional remarks about refluxing is particularly relevant to the Pine Island Ice Sheet, PIIS, calving event; because a lot of ice mass melted from the Pine Island Glacier, PIG, and then refroze at the edge of PIIS, where it just calved off.  However, at the risk of adding to your confusion: (a) You need to decide whether PIIS is just a floating extension of PIG or whether it is a seperate feature (ie: is the reflux happen within one body, or from one body to a different body); and (b) You need to decide by "move" do you only mean glacial ice movement, or do you mean ice mass loss (which can also occur not only by calving, but also by such means as: (i) basal melting and discharge; (ii) surface melting [including solar induced or rain induced] and run-off; (iii) wind scour of firn; (iv) sublimation; etc.).  In the way of examples: (a) If you are wondering why mountain glaciers are generally retreating worldwide, it is not because gravity is making them calve into the sea faster; it is because they are thermally melting; (b) If you are wondering why the PIG grounding line is retreating so fast, it is both because of advective melting from warm water, as well as because the flow of the glacial ice is causing the glacier to thin locally, which when it thins enough (both due to gravity flow and thermally induced basal melting) will cause the glacier ice to float thus transforming that portion of the glacier into an ice shelf; or (c) If you are only wondering about why the fracture of the PIIS iceberg calving occurred where it occurred and why it occurred at all, that is a combination of such factors as: ice shelf flow, water movement (including: advection, waves, tides and currents); ice shelf geometry (including the edge thickening due to reflux by refreezing); ice strength; internal stress patterns (including stress concentrations and thermal stresses); land boundary constraints; restraint from sea ice (as we have seen this is small); wind drag (and/or barometric pressure); etc.

As Peter Ellis points out it is possible to overthink such matters; but identifying which action controls the phenomena that you are interested in learning about; can depend on which question you are asking (and I point this out because I think that many seasoned researchers ask themselves questions relevant to the Northern Hemisphere, or to Mountain Glaciers, rather than the Southern Hemisphere ice sheets; which to some degree is why AR4's SLR projections have been proven to be so wrong and also why [before AR6 is issued] many of the AR5 SLR projections to be annouced in Sept 2013 will also be proven to be incorrect) .

Best,
ASLR
Title: Re: PIG has calved
Post by: Yuha on July 24, 2013, 06:21:24 PM
There's a new infrared image of the crack from July 14:

http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=81674 (http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=81674)

I can't really tell if there's been any change during the 6 days.
Title: Re: PIG has calved
Post by: AbruptSLR on August 06, 2013, 04:53:29 PM
The linked information indicates that as of August 1st the iceberg has not moved significantly (but that in the austal summer researchers will take measurements to see whether the remaining PIG-PIIS ice velocities increase due to the lose of buttressing action from the new iceberg):

http://www.livescience.com/38606-antarctic-iceberg-staying-put.html (http://www.livescience.com/38606-antarctic-iceberg-staying-put.html)
Title: Re: PIG has calved
Post by: Apocalypse4Real on September 13, 2013, 02:42:57 PM
There is a new piece of research out this week in Science on channelized melting effects on the PIG. See:

Channelized Ice Melting in the Ocean Boundary Layer Beneath Pine Island Glacier, Antarctica

T. P. Stanton1,*,
 W. J. Shaw1,
 M. Truffer2,
 H. F. J. Corr3,
 L. E. Peters4,
 K. L. Riverman4,
 R. Bindschadler5,
 D. M. Holland6,
 S. Anandakrishnan4
 
+ Author Affiliations

1Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943, USA.
2Geophysical Institute, University of Alaska, Fairbanks, AK 99775–7320, USA.
3British Antarctic Survey, Cambridge, CB3OET, UK.
4Department of Geosciences and Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA 16802–2711, USA.
5Emeritus Scientist, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
6Department of Mathematics, New York University, NY 10012, USA.
 
↵*Corresponding author. E-mail: stanton@nps.edu
Abstract

Editor's Summary

Ice shelves play a key role in the mass balance of the Antarctic ice sheets by buttressing their seaward-flowing outlet glaciers; however, they are exposed to the underlying ocean and may weaken if ocean thermal forcing increases. An expedition to the ice shelf of the remote Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet that has rapidly thinned and accelerated in recent decades, has been completed. Observations from geophysical surveys and long-term oceanographic instruments deployed down bore holes into the ocean cavity reveal a buoyancy-driven boundary layer within a basal channel that melts the channel apex by 0.06 meter per day, with near-zero melt rates along the flanks of the channel. A complex pattern of such channels is visible throughout the Pine Island Glacier shelf.
Title: Re: PIG has calved
Post by: AbruptSLR on September 13, 2013, 07:59:30 PM
Thanks A4R,

The following links and commentary related to the research that you cite elaborates on this matter, and the main point of the extract from the following article is that Antarctic Ice Shelves subjected to warm CDW (in this case the PIIS) are less stable than researchers previously thought because the subiceshelf melting occurs non-uniformly, which tends to accelerate the break-up of the ice shelf (as we have recently seen with the major calving in the austral winter of 2013).  This has major implications to the Thwaites Ice Shelf and Ice Tongue:

http://www.scienceworldreport.com/articles/9456/20130913/warm-ocean-water-beneath-antarctic-glacier-melts-ice-unprecedented-rate.htm (http://www.scienceworldreport.com/articles/9456/20130913/warm-ocean-water-beneath-antarctic-glacier-melts-ice-unprecedented-rate.htm)

"Pine Island Glacier is a major outlet of the West Antarctic Ice Sheet. Yet in recent years, this ice shelf has rapidly thinned and accelerated. That's why researchers decided to take a closer look to see exactly what was causing this increased melting.
The researchers drilled holes in the ice in order to place a variety of instruments there. In addition, the scientists used radar to map the underside of the ice shelf and the bottom of the ocean. This allowed them to see how the ice shelf was melting.
It turns out that the ice is melting more rapidly from below. Why? The oceans are far warmer than they have been in the past, and water can transfer more heat than air. In addition, the terrain beneath the ice shelf consists of a series of channels. The floating ice in the channel has ample room beneath it for ocean water to flow in. The water melts of the ice beneath and cools, but the channels keep the water from staying long enough to become too cold; this, in turn, accelerates melting.
"The way the ocean water is melting the ice shelf is a deeply non-uniform way," said Sridhar Anandakrishnan, one of the researchers, in a news release. "That's going to be more effective in breaking these ice shelves apart.""

The following link leads to the news release cited above:

http://www.eurekalert.org/pub_releases/2013-09/ps-uom091213.php (http://www.eurekalert.org/pub_releases/2013-09/ps-uom091213.php)
Title: Re: PIG has calved
Post by: LRC1962 on October 04, 2013, 06:30:39 AM
Say that report on the channelization. The question I have is this: Do they mean that the ice in those locations are melting 9 times faster then they thought or that they do know how much the melt is and just have found out where the melt is occurring?
With the channelizing being confirmed, I had read in other reports theories of that happening, that would seem to add the the worries about  a faster collapse possible as that would possibly make things 'pop' when it brakes in the middle. What I mean by that is something like what happens if you are pushing against a rock with a stick and the stick brakes in half. The rock, ridge grounding the ice, does not necessarily move, but the force that is behind it certainly does.
Title: Re: PIG has calved
Post by: AbruptSLR on October 05, 2013, 03:25:52 AM
LRC 1962

They mean that previously they only had estimates of the average rate of sub-ice-shelf ice melting for the Pine Island Ice Shelf, PIIS, but now that they have direct measurements, they now see that the channelization creates areas with ice melting many times higher than their previous estimates of the average ice melt rate.  Certainly, having higher localized melting zones can weaken the PIIS faster than previously estimated, which can lead to more active/larger calving than previously estimated (as was observed earlier this summer).

Best,
ASLR
Title: Re: PIG has calved
Post by: J Cartmill on November 10, 2013, 07:08:57 PM
Great animation of PIG at Fairfax Climate watch.

http://www.fairfaxclimatewatch.com/blog/2013/10/pine-island-glacier-pushing-massive-berg.html (http://www.fairfaxclimatewatch.com/blog/2013/10/pine-island-glacier-pushing-massive-berg.html)

Looks like a new crack just upstream of the old one.

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/Antarctica_r03c02/2013312/Antarctica_r03c02.2013312.terra.250m.jpg (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/Antarctica_r03c02/2013312/Antarctica_r03c02.2013312.terra.250m.jpg)
Title: Re: PIG has calved
Post by: ggelsrinc on November 10, 2013, 08:22:30 PM
Great animation of PIG at Fairfax Climate watch.

http://www.fairfaxclimatewatch.com/blog/2013/10/pine-island-glacier-pushing-massive-berg.html (http://www.fairfaxclimatewatch.com/blog/2013/10/pine-island-glacier-pushing-massive-berg.html)

Looks like a new crack just upstream of the old one.

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/Antarctica_r03c02/2013312/Antarctica_r03c02.2013312.terra.250m.jpg (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/Antarctica_r03c02/2013312/Antarctica_r03c02.2013312.terra.250m.jpg)

OK, but I have questions. Notice those cracks are located in the main glacier feed! Has PIG calved off that amount of ice shelf which is moving to the sea or is it still the same cracks I've seen monitored by airplanes flying over it?

It should be obvious, based on your image that the cracks are in the main feed of the glacier behind them. The cracks aren't news and that glacier is watched. Is there evidence to support PIG calving and moving to sea, yes or no?
Title: Re: PIG has calved
Post by: J Cartmill on November 10, 2013, 09:24:11 PM
My main purpose in posting was to call attention to the FCW blog post and the NASA animation (I've included it here)

The images from the first post in this thread seem to show it has calved.(Also included)

The MODIS image now shows a third crack that just appeared this week.

Title: Re: PIG has calved
Post by: ggelsrinc on November 10, 2013, 10:14:47 PM
I don't see a difference in your image based on other threads about the ultimate process PIG will face. I'm one of those people who think it's their job to watch glaciers and ice shelves, like they're canaries in my coal mine. The prognosis for PIG is death, but has it happened yet? With my limited knowledge, I think that area is regularly visited by aircraft that would know and I don't see anything on the news about it yet.
Title: Re: PIG has calved
Post by: Yuha on November 12, 2013, 07:22:41 PM
The ice island is now definitely loose:
Title: Re: PIG has calved
Post by: werther on November 12, 2013, 10:54:46 PM
Yes Yuha, I just thought to do a late night check on MODIS and saw it happening through thin clouds. I just posted it on the ASIB too.
Action shifting to Antarctica?
Title: Re: PIG has calved
Post by: AbruptSLR on November 14, 2013, 03:51:04 PM
A nice video from NASA of the direct measurement of sub-iceshelf melting of PIIS can be found at the following website:

http://www.nasa.gov/content/goddard/warm-ocean-rapidly-melting-antarctic-ice-shelf-from-below/ (http://www.nasa.gov/content/goddard/warm-ocean-rapidly-melting-antarctic-ice-shelf-from-below/)

This video also shows the ice velocity of an unnamed glacier (sometimes called the SW Tributary Glacier) feeding ice into the Southwest corner of the Pine Island Ice Shelf, PIIS.  Thus my concern is that as the front of the PIIS continues to thin due to sub-iceshelf melting, it's calving rate will continue to accelerate, which could migrate the calving front back behind the location where the SW Tributary Glacier feeds into the PIIS.  If/when this happens the ice velocity flow rates for the SW Tributary Glacier will accelerate; which in-turn would likely contribute to the destabilization of the Eastern Shear Margin of the Thwaites Glacier; which might then accelerate it's contribution to SLR (in the near-term).
Title: Re: PIG has calved
Post by: idunno on November 15, 2013, 11:12:02 AM
Re: PIG has calved

Er, that would be PIG has farrowed; COW has calved.

Unless this is some transspecies Frankenscience experiment going on.

I'll get me coat.

;)
Title: Re: PIG has calved
Post by: J Cartmill on November 15, 2013, 02:05:16 PM
Matt Owens has a new update at Fairfax climate watch with some inputs from Dr. Richard Alley
http://www.fairfaxclimatewatch.com/blog/2013/11/massive-pig-iceberg-breaks-free.html (http://www.fairfaxclimatewatch.com/blog/2013/11/massive-pig-iceberg-breaks-free.html)


High resolution views here:
http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=82392 (http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=82392)
Title: Re: PIG has calved
Post by: AbruptSLR on November 26, 2013, 04:54:28 PM
While I am not certain, the attached MODIS image from Nov 26th seems to show some local calving from PIIS:
Title: Re: PIG has calved
Post by: ggelsrinc on November 26, 2013, 06:28:36 PM
I'd be very interested in a study of historical ice shelves and a documentary of their collapse. I think it speaks without question for what our future will become.
Title: Re: PIG has calved
Post by: J Cartmill on December 06, 2013, 01:47:54 PM
More calving.

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Antarctica_r03c02.2013338.terra.1km (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Antarctica_r03c02.2013338.terra.1km)
Title: Re: PIG has calved
Post by: AbruptSLR on December 10, 2013, 02:10:27 AM
It appears to me (see Modis image from Dec 9, 2013) that the PIIS is calving small bergy-bit at a faster rate than in the past.  If this is the case, and if this trend continues, then it is possible that in the next few years that the rate of ice flow of the SW-tributary glacier (on the westside of PIIS) could accelerate by a factor of 3 to 6 (based on historical behavior of similar glaciers whose ice shelf buttressing was removed); which in-turn could reduce the stability of the adjoining Thwaites Glacier.
Title: Re: PIG has calved
Post by: crandles on December 10, 2013, 12:22:34 PM
Sounds like quite a few ifs there.

Isn't it more likely that these are weaknesses / additional cracks from when the crack worked its way though prior to the calving? Don't we have to wait much longer before such features of the cracking are clearly gone before talking about an increased calving rate?
Title: Re: PIG has calved
Post by: AbruptSLR on December 10, 2013, 04:36:51 PM
candles,

What level of "proof" one needs before taking action depends a lot on what type of action one intends to take.  The NRC 2013 has already advised policy makers that the risk of abrupt SLR from the WAIS this century is plausible/credible; which should encourage policy makers to adopt a resilency approach to planning for SLR, as a resilency approach does not require a high degree of "proof", as opposed to a 1% probability strength design event which typically requires a higher level of "proof".

While I admit that it is possible that the local calving (indicated by changes in the ice shelf face) could well be due to residual/secondary cracking from the major calving event document at the start of this thread, and that it is possible that the rate of local calving may soon slow-down; however, I believe that it is more likely that the local calving for PIIS will continue to accelerate in the near future for reasons including: (a) the shear boundary of the PIIS is currently more cracked-up and is likely to become more cracked-up as the ice shelf continues to thin, and the ice flow rate continues to accelerate, due to sub-ice shelf melting from the advection of CDW; (b) measurements of the sub-ice shelf melting have demonstrated that this melting is not uniform, resulting in sub-ice shelf grooves/stress-concentrations that promote calving; (c) the changes in the local wind patterns are promoting (measured) increased upwelling induced advection of warm CDW into the ASE; and (d) tidally induced flexure induces more calving of the current thin shelf face than of the former thick shelf face (note that frazil ice slowly accerates to the bottom of the ice shelf near the shelf face, so the major calving removed a thick section of shelf, and the current continued minor/local calving continues to remove thickening sections of shelf).

When one is faced with inherent "deep-uncertainty" one can choose to wait and see what happens (ie procrastinate), or one can choose to take precautionary measures such as establishing an early warning system (as recommended by the NRC 2013 abrupt climate change report), or taking resilency measures against potentially negative consequences.
Title: Re: PIG has calved
Post by: AbruptSLR on December 15, 2013, 03:52:01 PM
The following link leads to an article about research to study how ASE ice shelves have been and continue to lose their grip on the coastlines of the embayment.  Specifically, the accompanying image (from the website) illustrates how rifting (cracking) of the Pine Island Ice Shelf, PIIS, has increased from 1973 to 2011, while comparing the shape of the 2011 calving face with the current calving face (see prior posts in this thread), shows how rapidly the calving has accelerated in the past two years (as compared to the 1973 to 2011 period).  This provides support to my proposal that this trend of increasing cracking will lead to increasing calving of PIIS over the next few years:

http://www.research.gov/research-portal/appmanager/base/desktop;jsessionid=0R22SySYfBp1vN1LFqpJYkZxG4rM6zWMKkTTP6kp1QP47Sk072gQ (http://www.research.gov/research-portal/appmanager/base/desktop;jsessionid=0R22SySYfBp1vN1LFqpJYkZxG4rM6zWMKkTTP6kp1QP47Sk072gQ)!-1826466010!941996275?_nfpb=true&_windowLabel=awards_1&_urlType=action&wlpawards_1_id=%2FresearchGov%2FAwardHighlight%2FPublicAffairs%2F23322_WestAntarcticiceshelvesslip-slidingaway.html&wlpawards_1_action=selectAwardDetail
Title: Re: PIG has calved
Post by: AbruptSLR on December 21, 2013, 03:40:57 PM
While we may need to wait for the clouds to clear in order to make a definitive statement on this matter, but it appears clear to me from the attached image (from LANCE) comparing the PIIS on Dec 21, 2013 to Dec 19, 2013; that a very significant about of calving has occurred between these dates (primarily on Dec 20) in the area of high rifting that I indicated in my immediately preceding post.

If this observation is correct, this is potentially bad news as this high rifting area appears to contain a large amount of cracks and continued calving of bergy bits may continue throughout this austral summer.  If this were to happen then it is conceivable that the SW Tributary Glacier could lose its buttressing support from the PIIS, and its rate of ice flow could accelerate several times (say 5 times); which should then reduce the stability of the Thwaites Eastern Shear zone.
Title: Re: PIG has calved
Post by: AbruptSLR on December 21, 2013, 03:51:47 PM
For those having trouble identifying the area of rifting that I am referring to, it is clearly visible in the upper portion of the attached TerraSAR-X image from July 8, 2013.
Title: Re: PIG has calved
Post by: Shared Humanity on December 21, 2013, 09:25:43 PM
For those having trouble identifying the area of rifting that I am referring to, it is clearly visible in the upper portion of the attached TerraSAR-X image from July 8, 2013.

Sure looks like the glacier is losing its grip on land. Could that explain the curve in the calving front as well as the two pronounced calving fronts near the rifting?
Title: Re: PIG has calved
Post by: AbruptSLR on December 22, 2013, 12:34:50 AM
Shared Humanity,

Yes, this pattern of calving is clearly due to shear cracking which is causing the Pine Island Ice Shelf to gradually lose its grip on land.  The attached image comparing the afternoon of Dec 19th to the afternoon of Dec 21, 2013 more clearly shows the recent calving (and where I expect calving to continue during this austral summer).
Title: Re: PIG has calved
Post by: AbruptSLR on December 22, 2013, 01:09:43 AM
The attached image comes from NASA's WorldView:

https://earthdata.nasa.gov/labs/worldview/

This image shows a different angle of the site of the calving that occurred on Dec 20, 2013
Title: Re: PIG has calved
Post by: AbruptSLR on December 22, 2013, 01:15:15 AM
For comparison to the Dec 21, 2013 WorldView image in my immediate prior post, accompanying is the same view taken on Dec 19, 2013.
Title: Re: PIG has calved
Post by: MOwens on December 22, 2013, 01:57:26 AM
new Google Maps are just out, if you have a Google+ account, you can take a look (I'm pretty sure).

There are some VERY cool features in the maps, including PIG. You can tilt the map, and there is a high-definition view of the entire crack before the berg calved....other features worth seeing are Greenland and Antarctica in general. The tilt feature took a little time to get the hang of, but was otherwise easy.

I posted some screenshots here: http://www.fairfaxclimatewatch.com/blog/2013/12/new-google-maps-makes-getting-lost-fun.html (http://www.fairfaxclimatewatch.com/blog/2013/12/new-google-maps-makes-getting-lost-fun.html)

and here's two from Antarctica:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.fairfaxclimatewatch.com%2Fimages%2F2013_Google_Earth%2FAntarctica%2520Pine%2520Island%2520Glacier.jpg&hash=08df9a075227de163231a7249c0e875d)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.fairfaxclimatewatch.com%2Fimages%2F2013_Google_Earth%2FWest%2520Antarctic%2520Mountains3.jpg&hash=0faa08f6b5339de21b02a7c49be8d386)
Title: Re: PIG has calved
Post by: AbruptSLR on December 22, 2013, 06:27:21 PM
The attached image from LANCE taken on Dec 22, 2013 shows the recent calving area without any cloud cover (as verified by the the infrared image).  This image not only shows the extent of the recent calving, but also shows the adjoining shear cracking that will likely lead to more calving in this area as the austral summer progresses:

Title: Re: PIG has calved
Post by: AbruptSLR on December 23, 2013, 03:56:34 AM
I thought that this Dec 22, 2013 WorldView image of the recent (12/20/13) calving area was worth posting.
Title: Re: PIG has calved
Post by: AbruptSLR on December 26, 2013, 06:10:52 PM
It looks to me like snow is being blown off (or is sliding off) of the top of the high shear zone of PIIS into the ocean in this Dec 26 2013 LANCE (Terra) image.  Furthermore, it looks to me like this loss of snow cover is forming a deep long trench in the snow in the high shear zone of PIIS.  In the worst case scenario, as surface temperatures warm during this austral summer, the loss of the insulation from this lost snow cover could potentially accelerate surface ice melting in this cracked-up area which could lead to surface melt water flowing into the local crevasses, which would promote further calving in this sensitive area of PIIS; which in turn could accelerate the flow velocity of the indicated SW Tributary Glacier.
Title: Re: PIG has calved
Post by: AbruptSLR on December 28, 2013, 02:07:30 AM
While there is some cloud cover (so the view is not clear), it looks to me that the accompanying Terra (LANCE) image from Dec 27th shows some minor calving in the notch in the Northeast calving face as compared to the Dec 26th image that I posted yesterday.
Title: Re: PIG has calved
Post by: AbruptSLR on December 30, 2013, 06:44:08 PM
From the attached image it is not clear whether the new approximately 25km long float ice debris field/tongue and the associated new approximately 30km long trough in the snow above PIIS, is due to a local calving event and/or an avalanche of snow (possibly assisted by wind scour).  Nevertheless, this image shows a large scale dynamic event; which, does not speak well for the stability of the local face of the Pine Island Ice Shelf, PIIS.
Title: Re: PIG has calved
Post by: steve s on December 30, 2013, 09:12:30 PM
I suspect the image is of a cloud and shadow cast on a snow and water background..
Title: Re: PIG has calved
Post by: AbruptSLR on January 06, 2014, 01:50:10 AM
While it is possible that the image that I posted on Dec 30, 2013 may have some cloud cover over the PIIS; it is now my opinion that the approximately 25km streak in the ocean is probably snow blown (scoured) into the ocean by katabatic wind.

The attached image from January 5, 2014 indicates: (a) that between Dec 30th and January 5th there has been a good amount of snowfall over the PIIS, sufficient to fill-in snow blown into the ocean by katabatic wind, but not sufficient to fill-in any trough from an avalanche (therefore I conclude that no avalanche occurred on Dec 30th); and (b) there is clear signs of continued calving in the northeast notch in the PIIS, in the area of high shear cracking, and it is particularly in this area that I am concerned about continued calving throughout the current austral summer:

Title: Re: PIG has calved
Post by: AbruptSLR on January 06, 2014, 02:23:28 AM
In regard to my earlier post today, I thought that some people would like to see the attached infrared Terra image from January 5 2014, indicating that there are no clouds in this area on this date.
Title: Re: PIG has calved
Post by: Andreas T on January 07, 2014, 10:02:58 PM
There is weather data available from PIG http://efdl_5.cims.nyu.edu/timeseries/NYU_AWS_PIG_timeseries.html (http://efdl_5.cims.nyu.edu/timeseries/NYU_AWS_PIG_timeseries.html)
snow depth data looks odd, not sure what that means, could this be caused by snow blown into drift or cleared by wind?
Title: Re: PIG has calved
Post by: AbruptSLR on January 07, 2014, 11:03:18 PM
Andreas T,

Thank you for the link.  If the snow data is correct then the wind is the only explanation that I can think of as to why the snow depth changes so much.

Also, in the attached infrared image, it looks to me that the northeast portion of the notch is slightly larger as of Jan 7, 2014:
Title: Re: PIG has calved
Post by: AbruptSLR on January 12, 2014, 02:11:23 AM
In order to provide more context to the implications of the cracking behavior of the PIIS, I would like to briefly discuss the interaction between the El Nino Southern Oscillation, ENSO, trends and some of the recent major cracking/calving behavior:

The first attached image should the correlation of the recent ENSO and the mean global temperature anomaly until January 2013 (since then ENSO has been in the "neutral" range).

The second image for early February 1992 shows a major crevasse parallel with the SW Tributary interface (note the streak lines show ice movement from Feb to Dec 1992).  By examining the first image it can be seen that this major calving event occurred during a relatively strong El Nino period, when more CDW is advected beneath PIIS. Subsequent major calving events until 2013 all occurred with major crevasses roughly parallel to the SW Tributary Glacier interface (I suspect due to tension fields in the ice associated with: (a) the reduction in lateral restraint as the face of the ice shelf moves out into the ASE; (b) tidally induced flexural on the PIIS; and (c) compression, membrane shear and associated tension fields due to the SW Tributary Glacier ice flow interaction with the PIIS ice flow).

The third image taken in late November of 2011, shows both a major crevasse and shear crack zone that formed in October 2011 (about a year after the moderately positive ENSO index in 2010, see the first image).  The October 2011 major crevasse occurred several kilometers further upstream than normal (possibility due to deteriorating/thinning/rutting condition of the PIIS); however, the major calving event associated with the indicated crevasse did not happen until November 2013; and I believe that this two year delay from cracking to calving is likely due to the relatively cold water advected beneath PIIS due to the relatively strong La Nina event of 2011 (see the first image).

The fourth image shows both natural light and infrared images of the PIIS on Jan 11 2014, showing continuing calving in the northeastern notch area associated with the extensive shear cracking zone shown in the third image.  The fact that the calving in this notch area is continuing to extend upstream of the SW Tributary Glacier interface area (possibly due to the ENSO neutral condition melting the weak ice that probably formed in the shear cracks following the 2011 La Nina event), implies to me that the next major flexural/tension crevasse will likely occur still further upstream from the SW Tributary Glacier interface area than the location of the October 2011 crevasse formation.  If I am correct then there is an increasing risk that the buttress support from PIIS on the SW Tributary Glacier will degrade relatively rapidly, particularly if a major El Nino event occurs within the next few years.
Title: Re: PIG has calved
Post by: AbruptSLR on January 17, 2014, 01:00:51 AM
For those who are not certain where the current grounding line is for the Pine Inland Glacier (particularly with reference to the notch created by the recent calving activity), I provide the attached Lance-Modis image:
Title: Re: PIG has calved
Post by: AbruptSLR on January 17, 2014, 03:47:30 AM
For those who would like to compare the changes in the Pine Island Glacier, PIG, grounding and the Pine Island Ice Shelf, PIIS, extent shown in my immediate last post with both the first attached Landsat image from October 2009 and the second attached image of the associated bathymetry (gathered from October to November 2009), I provide the following:
Title: Re: PIG has calved
Post by: AbruptSLR on January 18, 2014, 06:34:47 PM
The attached natural light and infrared images for PIIS from January 18, 2014 (from Terra) indicate that a small amount of calving is continuing to occur in the notch (note the small ice debris field floating in the seawater in the notch).  This indicates to me that small calving events may continue to occur within the notch on a weekly basis throughout the austral summer:
Title: Re: PIG has calved
Post by: johnm33 on January 18, 2014, 07:39:26 PM
Deep Octopus put this link up elsewhere Pine Island Glacier has reached a point of no return. http://www.bbc.co.uk/news/science-environment-25729750 (http://www.bbc.co.uk/news/science-environment-25729750)
Title: Re: PIG has calved
Post by: johnm33 on January 19, 2014, 08:13:23 PM
The grounded berg in Pine Island Glaciers  bay is on the move, anyone know the tidal range, or where I can find it?
Title: Re: PIG has calved
Post by: Andreas T on January 19, 2014, 10:21:35 PM
this has low resolution but seems to make it unlikely to find high tidal range there
http://en.wikipedia.org/wiki/File:M2_tidal_constituent.jpg (http://en.wikipedia.org/wiki/File:M2_tidal_constituent.jpg)
Title: Re: PIG has calved
Post by: AbruptSLR on January 20, 2014, 05:17:01 AM
If you accept this sea ice concentration map from the Breman University, then as of today the local sea ice will no longer obstruct the introduction of storm waves into the Amundsen Sea Embayment, ASE:

Title: Re: PIG has calved
Post by: AbruptSLR on January 23, 2014, 05:11:48 PM
Andreas T,

While you are correct that the ASE generally has a low tidal range, according to the following reference the M2 tide component can have a significant effect on ice mass loss from glaciers around the Amundsen Sea (depending on the local specifics, see the accompanying Table 1 and conclusions from the linked article)

"Tides, Critical Latitude, and their Effects on the Amundsen Sea Ice Shelves", by Robin Robertson (2013) Exchanges, No. 62 (Vol 18 No.2) August 2013, CLIVAR; which can be found in the pdf at the following link (all the other papers are good, but are not as key to ASLR):

http://www.clivar.org/sites/default/files/Exchanges/Exchanges62.pdf (http://www.clivar.org/sites/default/files/Exchanges/Exchanges62.pdf)

Conclusion: "Tides have been shown to play a significant role in ice shelf melting and circulation under the ice shelf in strong tidal regimes, such as the Ross and Weddell Seas, through the mechanisms of tidal rectification and mixing [Makinson, et al., 2011; Mueller et al., 2012]. Here, tides are shown to play a significant role in even in weak tidal regimes for ice shelves near the effective critical latitude. Selected ice shelves along the Antarctic Peninsula, in the Weddell Sea, and Greenland, which are near the M2 critical latitude, are likely to respond similarly. Tidal effects on the ice shelves in these areas near critical latitude result from internal tides, increased baroclinicity, resonance effects, increased mixing, and non-linear effects on the density-driven circulation, rather than tidal residual velocities. These effects can increase ice shelf melt rates by 25-50%."
Title: Re: PIG has calved
Post by: AbruptSLR on January 25, 2014, 07:14:15 PM
The attached image (from January 24, 2014) shows that the iceberg that calved from PIIS in November 2013 is clearly on the move (it was previously grounded until recently), and is very near the Thwaites Ice Tongue.  The image also shows that: (a) the notch in PIIS looks a little bit larger; and (b) most to the land-fast sea ice around the Thwaites Ice Tongue appears to be breaking-up rapidly.
Title: Re: PIG has calved
Post by: steve s on January 25, 2014, 08:16:01 PM
The Thwaite's Tongue area is worth following closely; or rather the area between the Thwaite's Tongue and the PIG outlet. On December 26th a set of crevasses appeared, they were not visible on the previous day's image:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Flance-modis.eosdis.nasa.gov%2Fimagery%2Fsubsets%2F%3Fproject%3Dantarctica_regions%26amp%3Bsubset%3DThwaites_Tongue.2013360.terra.500m.jpg%26amp%3Bvectors%3Dnone&hash=ee96457d9e62fa1c15b9fd60f1b8dd0c)

For a sense of scale, (1) the grounded PIG iceberg is visible offshore; and (2) each pixel is 500 meters, so the cracks are both sudden and wide. The area covered in this huge event is far larger than the iceberg.

The following day the new crevasses were indistinct, their walls having calved, filling them in. The shelf was grounded, so this single event added more to SLR than the PIG's iceberg separating had. The area has been breaking up bit-by-bit since, only recently with large areas of ice rafting away. The last clear image was January 18, but the clouds did not hide much on January 21:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Flance-modis.eosdis.nasa.gov%2Fimagery%2Fsubsets%2F%3Fproject%3Dantarctica_regions%26amp%3Bsubset%3DThwaites_Tongue.2014021.terra.500m.jpg%26amp%3Bvectors%3Dnone&hash=5e0649cfb3bbd338284386cbe0822e55)

Through the cloud cover one can see hints that in the four days since the continued loss of ice has been extensive, but no details. I was hoping to report a month to month comparison.

Title: Re: PIG has calved
Post by: AbruptSLR on January 26, 2014, 04:19:55 AM
steve s,

I believe that what you are referring to is sea ice floating away from Thwaites; which is not related to glacial ice mass loss.  This is a normal/annual event and does not contribute to SLR.

ASLR

Title: Re: PIG has calved
Post by: AbruptSLR on January 26, 2014, 12:18:44 PM
As the image that I posted yesterday had a fairly significant amount of cloud cover, I provide the accompanying image from today (Jan 26) showing the same points that I made yesterday, except that it is clearer what is sea ice and what is glacial ice around Thwaites.
Title: Re: PIG has calved
Post by: AbruptSLR on January 27, 2014, 06:43:54 PM
The two attached images show a medium size calving event in the notch area of PIIS for January 27th (note that the infrared image confirms that the ice debris field in the sea water of the notch is not a cloud).  Again, I expect such calving events in the notch area to continue throughout the austral summer (which is a clear indication of the fragility of the PIIS in this notch area):

Title: Re: PIG has calved
Post by: AbruptSLR on January 27, 2014, 08:04:18 PM
Also, comparing the attached image from January 26th to the images in my last post from January 27th; it appears to me that the northwestern face of the PIIS has moved seaward.  If so, this movement seaward could have caused vibrations that triggered the calving event shown in the January 27th images (however, I must say that at the resolutions provided by LANCE, I cannot be sure):
Title: Re: PIG has calved
Post by: AbruptSLR on January 28, 2014, 01:10:00 AM
As people seem interested in the January 27 2014 calving event, I decided to post the accompanying images of the event from this afternoon; which when compared to this morning's images gives an idea of how far the ice debris field has moved in only a few hours:
Title: Re: PIG has calved
Post by: AbruptSLR on January 29, 2014, 02:02:31 AM
While I cannot say for sure, it is possible that the attached Aqua image of PIIS from January 28 2014, may indicate further calving activity:
Title: Re: PIG has calved
Post by: AbruptSLR on January 29, 2014, 04:12:55 PM
While a bit cloudy, this January 29, 2014 infrared Terra images makes clear to me that there was indeed another medium sized calving event in the eastern arm of the notch yesterday.  I would like to note that while calving is a natural event, this frequent of calving in this concentrated area is exceptional, and could contribute to stress concentration in the PIIS near the notch; which in turn could lead to another major calving event within the next few years.
Title: Re: PIG has calved
Post by: AbruptSLR on January 29, 2014, 09:51:30 PM
Although there is a little cloud cover, I think that this Terra image, from the afternoon of January 29, 2014, more clearly shows the extent of the calving yesterday than does the infrared image that I posted earlier today:
Title: Re: PIG has calved
Post by: AbruptSLR on January 31, 2014, 01:25:43 AM
The accompanying image from the NSIDC shows the Antarctic sea ice extent on January 29, 2014.  It is worth noting that the sea ice extent in the ASE is below normal for this time of year, which implies that more storm and wave action can access the glaciers around the ASE, including PIIS, more easily than normal, potentially resulting in more calving than normal:

http://nsidc.org/data/seaice_index/ (http://nsidc.org/data/seaice_index/)
Title: Re: PIG has calved
Post by: AbruptSLR on February 01, 2014, 04:13:45 AM
The attached image from late in the day on January 31 2014 by Aqua, shows what looks like a medium sized calving event in the notch, possibly triggered by motion of the PIIS:
Title: Re: PIG has calved
Post by: AbruptSLR on February 01, 2014, 01:18:21 PM
According to the air temperature information for PIG at the NYU link provided by Andreas T, the air temperature at PIG in the first part of January 2014 is warmer than the same period in 2013 (see attached figure):

http://efdl_5.cims.nyu.edu/timeseries/NYU_AWS_PIG_timeseries.html (http://efdl_5.cims.nyu.edu/timeseries/NYU_AWS_PIG_timeseries.html)
Title: Re: PIG has calved
Post by: Andreas T on February 01, 2014, 06:00:30 PM
The accompanying image from the NSIDC shows the Antarctic sea ice extent on January 29, 2014.  It is worth noting that the sea ice extent in the ASE is below normal for this time of year, which implies that more storm and wave action can access the glaciers around the ASE, including PIIS, more easily than normal, potentially resulting in more calving than normal:

http://nsidc.org/data/seaice_index/ (http://nsidc.org/data/seaice_index/)

although clouds allow only partial view of the sea surface, this modis image http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2014030232000-2014030232500.2km.jpg (http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2014030232000-2014030232500.2km.jpg) shows that some of those areas in the sea ice extent map have fairly dispersed ice in them. I guess that still has a dampening effect on waves.
Title: Re: PIG has calved
Post by: AbruptSLR on February 01, 2014, 07:31:18 PM
While there is some thin cloud cover in this image, it is clean to me that this image not only shows: (a) the extent of calving on the north face of the notch that occurred yesterday; but also; (b) the length of the arm of the notch that is extending in the northeastern direction is longer than yesterday morning, indicating that minor calving occurred on this northeastern face as well.  If it is not clear to the readers, calving on the northeastern face is particularly serious as: (a) the ice in this alignment is already fractured making more calving in this direction likely; and (b) calving along this alignment is more likely to contribute to a major calving event along the entire PIIS face (similar to what happened in Nov. 2013).
Title: Re: PIG has calved
Post by: crandles on February 01, 2014, 10:09:24 PM
I am wondering if the 2 large blocks indicated here:

http://farm6.staticflickr.com/5482/12256959813_6ba97da45d_m.jpg (http://farm6.staticflickr.com/5482/12256959813_6ba97da45d_m.jpg)

which seem visible on many such images are likely to be more solid than fractured ice near the open western ends of these blocks and are these blocks likely to work their way free?

If that were to happen, could the ice stream move more easily? Perhaps by changing direction slightly to the right because the eastern end would look more constrained then the western side? Is that a mis-interpretation of what I see or perhaps just wildly speculative?


original of image used is http://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=429.0;attach=4545;image (http://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=429.0;attach=4545;image)
Title: Re: PIG has calved
Post by: AbruptSLR on February 02, 2014, 12:09:59 AM
crandles,

The post that you made says that the flickr photo is currently unavailable, so I am not sure as to which 2 large blocks you are referring to.  Also, when you refer to east and west I am not sure what directions you are referring to as north is not at the top of the photos that I have posted.  Therefore, I have annotated the attached image from mid-January 2014, where I show a North Arrow, and I label two "blocks" that you might be referring to, and also a "pinnacle" marked with a red arrow that extends above the water plane (but below the top surface of the PIIS).  I refer to these features in my comments below:

The PIIS ice mass is clearly not homogeneous, and it clearly contains some blocks/sections that are stronger than others, and the boundary conditions for different portions of the PIIS also vary.  If what I labeled as blocks 1&2 were to calve off, then the "pinnacle" would offer less restraint to the PIIS (or ice stream); which in my opinion would make a major calving event more likely.  If that is what you are referring to, then I agree with you (but these are also just my wild speculations).

Best,
ASLR
Title: Re: PIG has calved
Post by: crandles on February 02, 2014, 12:38:35 AM
Sorry about the incorrect directions and missing photo. (Doesn't seem to be available here but if I click the link I have replaced it with, it does show for me but perhaps only me and I cannot find the image on flikr.

The pinnacle seems to be within block 1 making that rather less likely to free itself soon.

Thanks for the reply.
Title: Re: PIG has calved
Post by: AbruptSLR on February 03, 2014, 11:23:15 PM
It seems to me that these Terra (visible & infrared) images from February 3, 2014 show a little bit more calving in the northeast arm of the notch:
Title: Re: PIG has calved
Post by: AbruptSLR on February 04, 2014, 01:39:01 AM
Not to get carried away with too many photos, but the accompanying image by Aqua from the afternoon of Feb 3 2014 has clear skies, and appears more clearly to indicate that the northeastern arm of the notch is increasing in length due to minor calving at the end of the arm:
 
Title: Re: PIG has calved
Post by: AbruptSLR on February 05, 2014, 07:02:30 PM
As people seem to continue to download these images, I thought that I would post this infrared image from the morning of Feb 5, 2014 by Terra; which clearly indicates how long the arm (that is extending in the Southeast direction) of the notch is getting to be (please excuse the cloud cover):
Title: Re: PIG has calved
Post by: Yuha on February 06, 2014, 02:11:25 AM
There has been some recent small scale calving activity at the western part of Thwaites glacier too as shown in the following images from January 11, 17 and 27. The arrows point to the changes at the calving front.
Title: Re: PIG has calved
Post by: steve s on February 06, 2014, 08:37:06 AM
Anyone have an explanation for the ongoing open water at that one spot? It has been visible in images for at least the last two months despite being surrounded by what seems to be bergs. The bergs seem neither to shrink in size nearby (indicating melting) or to enter the open water.

If I read D in http://glacierchange.files.wordpress.com/2012/10/thwaites-bedrock-2.jpg (http://glacierchange.files.wordpress.com/2012/10/thwaites-bedrock-2.jpg) correctly, the open water is behind the 2009 oceanic grounding line and likely where a deep water location with ungrounded ice is indicated. Have suitable currents or geothermal heat sources been reported in that area?
Title: Re: PIG has calved
Post by: AbruptSLR on February 06, 2014, 04:38:31 PM
steve s,

I do not have time now for  a detailed reply but this is what I can say for now:

Regarding the open water, or polynas, the following text is from Wikipedia:

"Polynyas are formed through two main processes:
Sensible Heat Polynya: this is thermodynamically driven, and typically occurs when warm water upwelling keeps the surface water temperature at or above the freezing point. This reduces ice production and may stop it altogether.
Latent Heat Polynya: is formed through the action of katabatic wind or ocean currents which act to drive ice away from a fixed boundary, such as a coastline, fast ice, or an ice bridge. The polynya forms initially by the first year pack ice being driven away from the coast, which leaves an area of open water within which new ice is formed. This new ice is then also herded downwind toward the first year pack ice. When it reaches the pack ice the new ice is consolidated onto the pack ice. The latent heat polynya is the open water region between the coast and the ice pack.

Latent heat polynyas are regions of high ice production and therefore are possible sites of dense water production in both polar regions. The high ice production rates within these polynyas leads to a large amount of brine rejection into the surface waters. This salty water then sinks and mixes to possibly form new water masses."

While what you point to is not a large polyna, nevertheless, at this location there are both katabatic winds, and there is a local warm water current advected to this location coming from the PIIS/PIG (see my first few posts in the "Surge" thread).  Therefore, both wind and upwelling combined could account for the polyna.

Next, the first attached image of the Thwaites Ice Tongue (north is at the left of the image) is from Google Earth circa early December 2013, with the grounding line shown in turquois (note the longitude and latitude written on the image are at the "W" in Walgreen Coast on the image.  You can see that the old ice tongue iceberg that calved in October of 2012 (see the images and discussion in the "Surge" thread) is splitting away from the new ice tongue in the image, and the polyna that you refer to has not yet formed.

The second image shows some improved bathymetry in this area from the University of Texas  (published in 2013) with longitudes and latitudes, and scaled dividing lines, for your reference.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on February 06, 2014, 05:23:30 PM
To my immediate prior post, I now have time to add the two attached images from Google Earth of zoomed in images of the calving face on the west base of the Thwaites Ice Tongue from early December 2013 (you can use Google Earth yourself to zoom around this area):
Title: Re: PIG has calved
Post by: AbruptSLR on February 07, 2014, 02:03:50 AM
I decided to post this image of the PIIS for Feb 6 2014 by Aqua, not because it shows any new calving, but because it is cloud free and higher resolution then my last posted image.
Title: Re: PIG has calved
Post by: steve s on February 07, 2014, 05:01:39 AM
Aslr, thanks for your reply. However, I think further discussion is in order.

You mentioned and embedded Google Earth images. Google Earth and map images are updated infrequently. For example, T]the zoomed crevasse image you posted is dated 1/26/2010. The lovely image you report as being from early December 2013 is dated 12/31/1998, long before several calving events. The images' dates are printed along their bottom edges.

My preference is to use the MODIS Rapidfire daily image subsets for convenient comparisons. Because of the loss of historic images due to the failure of a disk that was not backed up, I cannot tell when the hole opened through. However photos dated December 2012, after the last major tongue retreat, do not show the hole. Thus the phenomenon is new and may be a coal-mine canary.

Whether it is a traditional polyna is in question. A polyna is usually associated with seasonal sea ice, not ice shelves. The area where this hole is occurring was reported to be an ice shelf until recently -- as was the area I mentioned in a previous post -- and, to my knowledge, has not had seasonal ice for a very long time. Clearly the shelf has broken up. but into bergs of fairly uniform size; apparently crevasse interval-determined width.

Polynas can be maintained by winds or currents, but winds work on bergs poorly because of their depth. In this case the open space is among tightly packed bergs.  More likely in my opinion is that an upwelling is keeping the hole open. You suggest from the PIG, but I suspect from under the Thwaites. In either case, it would seem to require a tremendous sustained flow, not the burst-emptying of a pond, to force bergs so far apart and then keep them away. Several mechanisms come to mind, one of which is geothermal melting somewhere under the Thwaites.

I don't have an answer to the cause of the open water, but I do wonder whether the TG's contribution to SLR is now higher than reported.

Title: Re: PIG has calved
Post by: Wipneus on February 07, 2014, 08:46:39 AM
Reading the posts, I thought this image might interest you.

The corner of interest is in the path of Landsat 8 roughly every 8 days. Images on January 11, 18 and 27 are appear relatively cloud free.
This is January 18, the other images are ordered from the USGS and I will make a sequence when available.

For now it looks that the debris that is visible is from sea ice formed between the ice bergs.

The image is processed to show natural color in with 15m resolution. Do not forget to click the attached image for the full resolution.
Title: Re: PIG has calved
Post by: AbruptSLR on February 07, 2014, 05:21:47 PM
steve s,

Thanks for the corrections about the Google Earth images (Google Earth seems to be a mosaic of images with different dates in different parts of the mosaic).

Wipneus,

Thanks for the high resolution Landsat 8 image from January 18, and I look forward to seeing the sequence when it is available.

Also, in order to focus future discuss between what is sea ice and what is glacial/ice shelf ice, and what changes have recently occurred in the ASE, I post the accompanying image from MacGregor et al 2012 which shows the recent history of changes in the ASE ice shelves, which helps clarify where the sea ice is and where the grounding lines are (although these are changing in real-time also).  In this regard: (a) the polyna that steve s is referring to appears to be in an area that is currently sea ice; and (b) the fractured ice in the Landsat 8 image is fractured glacial ice and not sea ice, between the two difference portions of the Pine Island Ice Shelf.
Title: Re: PIG has calved
Post by: AbruptSLR on February 07, 2014, 06:12:12 PM
I would also like to say that we should all remember that most of the processes (changes) that we are seeing today have been going on for many years now, but I (and many others) are concerned when this on-going processes result in fundamental change in future behavior, leading to sea level rise.

For example, the first image from Landsat in 2001 shows the same fracturing pattern in PIIS that Wipneus's post shows for 2014; however, the calving face has retreated back to the pinnacle that I referred to in my posts with crandles and should future local calving in the present day notch un-pin the many PIIS ice stream from the pinnacle then the calving face could retreat so far upstream that the SW tributary glacier ice flow accelerates and then reduces the stability of the Thwaites Glacier.

For another example, the second image from Landsat 7 from January 2013 (from
"A novel method for predicting fracture in floating ice" by: Liz LOGAN, Ginny CATANIA, Luc LAVIER, Eunseo CHOI; Journal of Glaciology, Vol. 59, No. 216, 2013, doi:10.3189/2013JoG12J210)  shows that the crevasse cracking in the ungrounded Thwaites Glacier is on-going, but Google Earth images that I posted show that similar cracks were occurring for many years now.  However, the Thwaites Ice Stream in this area is thinning rapidly and calving associated with the crevasse cracking that Logan et al 2013 discuss appear likely to accelerate in the future, especially, since most of the basal water existing from beneath Thwaites appears to be existing from this rapidly thinning area of ice stream.

Lastly, the third attached image of a computer model of warm water circulation in the ASE, supports that warm water does circulate underneath the area of the polyna that steve s refers to; but nevertheless, basal water leaking out from Thwaites would likely increase upwelling in this area; so who knows in any given year what processes does or doesn't clear-out the sea ice around the Thwaites Ice Shelve at any given time of year; I guess we will all have to watch and see how the patterns/processes change with time; but I am very concerned that during an El Nino event that the warm water circulation in and around both the PIG and the Thwaites Glaciers will accelerate grounding line retreat and ice mass loss.
Title: Re: PIG has calved
Post by: Wipneus on February 07, 2014, 06:40:15 PM
Some of those maps are right in time for me get acquainted with the geography around here, thanks you.

The 27 January image seems to take ages to process, while other images are returned within hours.

Here is a animation of Images from 1 December and 18 January. The calving is of course obvious, but you can also see the entire mass of ice has moved  by 27 pixels down and 18 to the left, or about 490 meters.

Of couse, without clicking nothing will animate.

[edit changed the estimated movement from 400->490 m (forgot to account the side wards movement)
Title: Re: PIG has calved
Post by: AbruptSLR on February 07, 2014, 07:25:58 PM
Wipneus,

Thank you for the great Landsat 8 sequence from 1 December 2013 to 18 January 2014, it exciting to have someone with your skill set adding to this folder.  It is great to be able to both more clearly see the fractured ice, and to see the face of the PIIS move outward with time.

Also, once all the sea ice clears out from around the base of the Thwaites Ice Shelf (and/or Ice Tongue), later this austral summer, I would expect the calving that steve s was referring to will accelerate; therefore, if you have time in the next few weeks if would be great to a similar sequence for the base of the Thwaites Ice Shelf as what you did for the PIIS, expect in the area shown in the LOGAN et al 2013, doi:10.3189/2013JoG12J210, image in my previous post.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on February 07, 2014, 10:58:44 PM
Following Wipneus' lead I went to the USGS website below and registered for access to the Landsat 8 & 7 images:

http://earthexplorer.usgs.gov/ (http://earthexplorer.usgs.gov/)

The attached image is near the base of the Thwaites Ice Shelf, and I believe at the bottom of the image (the western side of the image) we see the iceberg that calved from Thwaites in October 2012 breaking up (I believe I previously said that this area might be sea ice but it appears to be glacial ice) together with some new blocks calving from the ice shelf.  It will be interesting to see what this area and the PIIS look like by the end of this austral season.
Title: Re: PIG has calved
Post by: AbruptSLR on February 08, 2014, 09:51:27 PM
Hopefully, the attached images will clarify more issues, as opposed to creating more confusion:

The first image from Google Earth is a mosaic of images from different years/times (which can create confusion), and I only post it here because the turquoise line in this image shows the approximate location of the Walgreen Coast (part of the ASE) grounding line.

The second image is an annotated section of the Landsat image from January 30, 2014 of the area around the Thwaites Eastern Ice Shelf.  This image shows that after the late October 2012 calving event (see the "Surge" thread) that the Thwaites Ice Tongue has largely calved alway, while the image shows that the iceberg from the October 2012 calving of the Thwaites Ice Tongue is trapped by landfast sea ice just west of the Thwaites Eastern Ice Shelf and is slowly disintegrating.

The third image is from MacGregor et al 2013, and shows: (a) bathymetry and hand drawn ice shear boundaries and (b) the lateral shear strain rate showing how fast the ice velocity decreases laterally (at right angles to the direction of direction of ice flow).

The fourth image is from the University of Texas of ice flow velocities circa 2009 (note the MacGregor lateral shear strains split from right-handed to left-handed shear along the center line of this ice velocity flow lines), and note that this images shows the old iceberg from the circa 2011 calving event of the Thwaites Ice Tongue (that has since moved away).

Again, I hope that these images add some clarity rather that more confusion. 
Title: Re: PIG has calved
Post by: Wipneus on February 09, 2014, 04:02:36 PM
The Jan-27 that I ordered finally came in this morning.

The sequence shows quite visible the movement of the ice sheet, 9 pixels down and 6 to the left = 165 meter total.

The ground glacial ice between this ice and the ice fasted to the land is giving way. Some compression is visible between stationary ice to the lower half and ice moving with the pack more to the top.

Of course assuming that you did click the attached image.
Title: Re: PIG has calved
Post by: AbruptSLR on February 09, 2014, 06:36:48 PM
Wipneus,

Thanks for the very dramatic sequence from Jan 11, 14 and 27 2014.  This sequence does help to better understand the dynamics of this critical area of the Pine Island Ice Shelf, PIIS.  In addition to the observations that you make in your post about the relative motion of the ice stream (down is towards the west and left is towards the north, so the motion of Blocks 1 and 2 would be West by Northwest), and compression behavior in the ice stream; I add the following comments/observations:
(1) In past years similar "notches" have occurred but always further to the West by Northwest, thus indicating that the calving face of PIIS is retreating upstream, and once clear of the pinnacle that I previously discussed, the ice stream velocity, and probably the rate of calving, will likely accelerate. 
(2) At its current rate of movement "Block 1" should move beyond the "pinnacle" well before the end of this austral summer and thus may be subject to local calving this year.
(3) When looking at the MacGregor et al 2013 figure in my last post showing rate of change of lateral shear strain, it is clear that the shear restraint on both the right and left (note you look downstream when determining what is left and right) boundaries of the PIIS ice stream are still exerting shear restraint (possibly due to compression across fractured ice along the boundaries).

Lastly, I post the accompanying Modis/LANCE Terra images from Feb 9, 2014 showing that while there has been more calving in the notch since January 27, there has not been much, if any, calving in this area since Feb 6, 2014.

Also, as the side by side images are rather small, I post the natural light image from Feb 9 2014 separately:
Title: Re: PIG has calved
Post by: AbruptSLR on February 10, 2014, 04:47:33 PM
I just downloaded the accompanying Landsat images for Feb 8 2014, first for the notch for PIIS, and second for the Thwaites Eastern Ice Shelf, TEIS.  Note the significant amount of sea ice around TEIS is helping to prevent fractured portions of TEIS from calving.  As the austral summer progresses, this sea ice around TEIS may disappear; which may allow significant portions of TEIS to calve this year:

NOTE: I just modified the size of the first image (of the PIIS notch), and added a third enlarged image of TEIS
Title: Re: PIG has calved
Post by: AbruptSLR on February 11, 2014, 05:24:20 PM
While I cannot say with certainty bases on the Modis/LANCE images, but the attached Terra images from Feb 11, 2014, make it appear as though the PIIS ice stream has lurched forward (moved the ice face downstream), resulting in the displacement of floating fractured glacial ice from within the notch (or possibly a calving event from the face of the ice stream).  If the ice stream is moving this fast (i.e. if the images are not distorted), then it appears that ice mass loss from PIG is clearly accelerating in real time.
Title: Re: PIG has calved
Post by: AbruptSLR on February 11, 2014, 05:45:50 PM
As I found the apparent downstream movement of the face of the PIIS ice stream so exceptional from the Terra image on Feb 11 2014; I decided to post the Aqua image from earlier in the day from Feb 11 2014.  To my mind the apparent difference of the location of the face of the PIIS ice stream in the two sets of images, implies that Block 1 came unpinned from the pinnacle and surged forward.  As I am much more low-tech than Wipeus, I proved that attached image from Google Earth in the PIIS notch area (before the notch formed but after the November 2013 major calving event), with a 5km long line as a scale reference.
Title: Re: PIG has calved
Post by: AbruptSLR on February 11, 2014, 06:30:03 PM
Looking at the Terra images from Feb 11 2014, it occurs to me that a more reasonable explanation than the entire PIIS ice stream lurching forward, it that Block 1 probably has broken free from the PIIS ice stream, probably due to forces associated with its possible prior pinning on the pinnacle.  If so this would mean that ice mass loss from PIG need not be accelerating quickly; but would mean that the rest of the PIIS ice stream may be temporarily un-pinned from the pinnacle, and thus temporarily subjected to a higher risk of a major crevasse forming across the body of the ice stream, until the ice stream moves sufficiently downstream to become pinned again.  I guess that we will need to wait and watch as future images become available.
Title: Re: PIG has calved
Post by: AbruptSLR on February 12, 2014, 02:23:23 AM
Based on the attached images from Terra on the afternoon of Feb 11 2014, I conclude that what the morning images showed was a minor calving event of fractured ice from the west by northwest tip of Block 1.  It appear clear in these afternoon images that Block 1 is still attached to the PIIS Ice Stream (and is probably still pinned by the pinnacle), and that the PIIS Ice Stream did not lurch forward (even locally in the notch area).  Again, these images only indicate continuing local calving of fractured ice in and around the notch.
Title: Re: PIG has calved
Post by: Wipneus on February 12, 2014, 01:07:26 PM
Added Feb 10 to the sequence, a bit cloudy but the ice is quite visible. Estimated movement since Jan 27: 7 pixels down 6 left, about 138m. So no dramatic change in speed.

Click on the image for the animation.
Title: Re: PIG has calved
Post by: AbruptSLR on February 12, 2014, 05:34:23 PM
Wipneus,

Thanks for the great updated sequence.  I concur that most, or all, of the calving events that we are seeing from the notch appears to be fractured glacial ice debris that was sheared upstream as the PIIS ice stream flows west by northwestward.  Thus not indicating a general acceleration of the PIIS ice stream, and as similar notch have been seen in the past, the presence of the notch by itself does not bring into question the structural integrity of the PIIS ice stream.  Again, what I am mostly concerned about is that all previous notches were many kilometers towards the west by northwest, while this current notch is right near the pinnacle.  Thus as long as PIIS stream remained pinned by the pinnacle we can assume behavior similar to the past.

I believe that the attached Aqua image from February 12 2014 likely shows additional calving of previously fractured glacial ice debris from the northwest corner of the notch (i.e. from the non-ice-stream portion of the notch).  It seems likely to me that we are seeing so much calving activity (of fractured ice) because the ocean water is warmer than normal, thus forming the notch so far eastward, and we can reasonably assume that such warm ocean water is accelerating basal melting from PIIS causing it to thin faster than in the past.
Title: Re: PIG has calved
Post by: AbruptSLR on February 13, 2014, 07:10:03 PM
In the way of a status report, I thought that I would post these images from Terra for Feb 13, 2014, of the PIIS and the Thwaites Ice Shelf, respectively; although the images do not show much recent change:
Title: Re: PIG has calved
Post by: AbruptSLR on February 15, 2014, 01:19:16 AM
While there are some clouds in this image, it appears to me that the arm of the notch pointing eastward looks a little longer in this Feb 14, 2014 - Terra afternoon image.
Title: Re: PIG has calved
Post by: AbruptSLR on February 15, 2014, 04:26:02 AM
Landsat had this image available from Feb 10 2014, but I see very little differences in the ice from the Feb 8 2014 Landsat image that I posted earlier this week.  It will be interesting to see a Landsat image from after the Feb 11 & 12 calving events, when it (they) become(s) available.
Title: Re: PIG has calved
Post by: AbruptSLR on February 15, 2014, 07:40:41 PM
Comparing the accompanying Landsat image of the PIIS notch area from Feb 15 2014, with the Feb 10 2014 image in my last post, the areas of fractured glacial ice that have calved always on Feb 11 & 12 are clear (leaving the "arm" pointing eastward much longer.  But I am even more concerned that when comparing the Feb 10 and the Feb 15 images that the fissures around Block 2 look to have a growing amount of open water, which might portend a future calving of Block 2 this austral summer.
Title: Re: PIG has calved
Post by: AbruptSLR on February 15, 2014, 07:50:03 PM
Both of the Landsat images show the area around the iceberg that calved from the Thwaites Ice Tongue in October of 2012, which is now stuck in landfast sea ice.  The first image is from Feb 13 2014 and shows a major crack in the landfast sea ice to the west of the iceberg; which the second image from Feb 15 shows a large area of this landfast sea ice previously to the west of the iceberg has disappeared.  This does not necessarily mean that the iceberg will break free of the landfast ice this austral summer, but it clearly means that the relatively warm ocean water in this area is continuing to melt the local landfast sea ice.  It is my believe that if, and when, this iceberg finally does break free (possibly next austral summer if a big El Nino event happens at the end of 2014), this will expose the western side of the Thwaites Eastern Ice Shelf to accelerated calving.
Title: Re: PIG has calved
Post by: steve s on February 15, 2014, 09:09:48 PM
Thank you ASLR for posting these detailed images.

I've been watching that notch form and increase in size over the last few days, but using the less detailed MODIS images. How the notch could open to the extent it did without spilling visible ice into the ocean was difficult to understand. Apparently there are a pair of actions involved. The ice (which apparently was thin) crumbled, but remained along the other ice, apparently pinned by a current. The other action is a surface current flowing west under the ice which has shifted ice west opening that notch while closing the obvious crack in the first photo.

If one examines the movements of separating ice blocks along the coast between the Thwaites tongue and the PIG over series of images, the same current seems to be active.

Has to be a lot of water moving, possibly augmented by high flows through the Thwaites gateway. This area may prove interesting in the next week or so.

Title: Re: PIG has calved
Post by: Yuha on February 16, 2014, 03:33:28 AM
ASLR, I believe the iceberg in post #107 is not (just) stuck in landfast ice but is pinned on an underwater peak. In the figure below (from "Progressive unpinning of Thwaites Glacier from newly identified offshore ridge: Constraints from aerogravity" by Tinto & Bell, Geophysical Research Letters, Vol. 38, L20503, doi:10.1029/2011GL049026, 2011) the peak is labelled 2 in Figure C and is about 400-500 meters below surface according to Figure B.

The iceberg is actually moving slowly northwards, probably pushed by the remnants of the ice tongue. If so, the iceberg may be slowing down the flow of Thwaites at least a bit. Sometime fairly soon, within a few years, either the iceberg advances past the peak and sails away, or the ice tongue breaks down and stops pushing the iceberg. Either event could speed up the flow of Thwaites, which is a scary thought as that part of Thwaites is already the fastest moving part and also where the Byrd Subglacial Basin comes closest to the Thwaites grounding line.
Title: Re: PIG has calved
Post by: AbruptSLR on February 16, 2014, 04:16:45 AM
Yuha,

I believe that you are correct; however, I think that the coordinates Tinto & Bell show on their drawings are not very precise.  In any event with the top of the pinnacle labeled 2  is shown as being between -400 and -500m, and as the old ice tongue was thinning with time, it may be that this new iceberg is easier to dislodge as compared to prior icebergs that where temporarily pinned on this pinnacle 2.  Also, I note that MacGregor et al 2012 states that that the buttressing action from the stunted Thwaites Ice Tongue was not as significant as some earlier researchers had suspected.

We will all need to wait to see what happens in this area with time in the warming ocean of the ASE. 

Thanks,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on February 16, 2014, 06:16:40 AM
For those who are interested, I am posting the attached image of the Thwaites Ice Tongue Iceberg (and of the Thwaites Eastern Ice Shelf) in this Modis image from Feb 8 2013; however, the image is rotated 90 degrees from the other images of this area in this thread.  It can be seen in this image that all the currently extant ice to the west of the Thwaites Ice Tongue Iceberg is sea ice, as in Feb 2013 all of this area was open water.  This supports Yuha's statement that the iceberg is pinned by the pinnacle labeled 2 by Tinto & Bell, and not by the sea ice. 

Nevertheless, it is also clear from the Feb 8 2013 image that the ice south of the iceberg was gradually calving blocks of bergy bits, and this local calving of blocks of bergy bits could accelerate if this sea ice to the west of the old Thwaites Ice Tongue disappears in the future (maybe next austral summer).
Title: Re: PIG has calved
Post by: AbruptSLR on February 16, 2014, 12:18:18 PM
Further to my last post about the Thwaites Ice Tongue Iceberg, I provide the first image from Modis March21 2013 (where north is at the top of the image), and also the second Terra image from Dec 11 2013 (where north is at the left of the image).  This gives more information about the changes (timing & location) in the local sea ice, and the gradual calving of small blocks of glacial bergy bits.
Title: Re: PIG has calved
Post by: AbruptSLR on February 16, 2014, 11:45:32 PM
I provide a series of weblinks and the two attached images to give those who are interested a better back story about the major 2012 calving event for the Thwaties Ice Tongue that has left it roughly in the configuration that it is in today.


The first link is to a weblink dated Oct 8 2012, but which has been updated periodically since that date.  It presents the most comprehensive back story to the 2012 Thwaites Ice Tongue calving event, and was the inspiration for my "Surge" thread (which concludes that the 2012 surge of the Thwaites Ice Tongue appears to in-filled the subglacial cavity discussed by Tinto & Bell, 2011).  This website is also the source of the first attached image from Feb 2012 showing the Thwaites Ice Tongue and Ice Shelf prior to the calving event, while the second attached image from Sept 2012 shows this area after the calving event.  This website also has embedded the related video by Mauri Pelto also referenced in the second link below:

http://glacierchange.wordpress.com/2012/10/08/thwaites-glacier-tongue-major-calving-event-antarctica/ (http://glacierchange.wordpress.com/2012/10/08/thwaites-glacier-tongue-major-calving-event-antarctica/)

The following links directly to a YouTube video by Mauri Pelto about the 2012 calving event from the Thwaites Ice Tongue

https://www.youtube.com/watch?v=DWYIM29xNzk&feature=player_embedded (https://www.youtube.com/watch?v=DWYIM29xNzk&feature=player_embedded)

The following links to a NOAA article about the 2002 calving of iceberg B-22 from the Thwaites Ice Tongue
http://www.noaanews.noaa.gov/stories/s879.htm (http://www.noaanews.noaa.gov/stories/s879.htm)
P.S.: I also am modifying this post to attach a third NOAA image from March 2002 of the B-22 iceberg.

The following links to the WAIS 2013 Workshop thread, where: (a) reply #11 talks about the change in surface elevation of the Thwaites Glacier near the grounding line of the Thwaites Ice Tongue to the the 2012 major calving event; and the crevasse cracking pattern in that same area with a depressed surface elevation; and (b) reply #17 talks about a March 2011 calving event which I speculated might have weakened the Thwaites Ice Tongue sufficiently to trigger the major 2012 calving event:

http://forum.arctic-sea-ice.net/index.php?topic=694.0 (http://forum.arctic-sea-ice.net/index.php?topic=694.0)


I hope that this back story makes it clear that there have been a series of icebergs calved from the Thwaities Ice Tongue in the past, which have floated away; while the iceberg that I have most recently been referred to as being pinned by the pinnacle 2 (per Tinto & Bell, 2011), has never floated freely, but which has clearly broken off from the ice tongue as the crevasse pattern in its surface is rotated away from the crevasse pattern visible in the residual ice tongue (now broken into a bunch of approximately 1km by 1km blocks) and in the recently thinned portion of the Thwaites Ice Stream feeding into the residual ice tongue.
Title: Re: PIG has calved
Post by: AbruptSLR on February 17, 2014, 12:07:45 AM
In the way of a status report, I post the accompanying four images all from Feb 16 2014 from Terra, with the first two images being of Thwaites and the second two images being of PIIS:
Title: Re: PIG has calved
Post by: AbruptSLR on February 17, 2014, 10:57:09 AM
I am posting this magnified image of the residual Thwaites Ice Tongue (the area east of the polyna), to emphasize the following points:
(1) While Yuha is correct that this highly fractured ice zone is in compression (between the northward flow of the local Thwaites ice stream and the iceberg pinned on pinnacle 2) still: (a) when comparing this image from Feb 13 to the Feb 16 image in my prior post, it can be seen that one small bergy bit has dislodged from the southeast corner of the polyna, indicating that this small corner of the residual ice tongue was not in compression, otherwise the bergy bit could not have floated away; (b) the residual ice tongue is pushing the pinned iceberg at an angle, causing the pinned iceberg to slowly rotate, which should cause the pinned iceberg to dislodge from the pinnacle more easily, given enough time (possibly by the next austral summer); and (c) one the pinned iceberg dislodges, there will be no new iceberg from the residual ice tongue to take its turn being pinned on pinnacle 2, as the residual ice tongue is so fractured, that when the compressive stress in it is relieved by the iceberg floating away (in the future) then the ice tongue will likely fragment rapidly into individual bergy bits.
(2) The local conditions around the Thwaites residual Ice Tongue and Eastern Ice Shelf are becoming more conducive to the fragmentation of these ice features due to: (a) the increasing ocean water temperatures, which causes continuing basal ice melting of these features; (b) the eastern face of the Thwaites Eastern Ice Shelf has recently calved a few relatively large ice blocks from its eastern face, indicating it is also degrading together with the ice tongue; and (c) when looking a the findings of MacGregor et al 2012, it is clear that the rate of major calving events for the Thwaites Ice Tongue has been accelerating in recent years.
(3) The melt conditions in the ASE look likely to be worst next austal summer than in recent years due to: (a) the healing ozone hole should move the ABSL from its current location closer to the Ross Sea back eastward toward the ASE; (b) an El Nino event is likely by the next austral summer; and (c) it seems likely to me that what I called "horizontal advection" between PIG and Thwaites appears to be strengthening as the basal melting in PIG/PIIS is accelerating thus directing more warm CDW towards Thwaites.
Title: Re: PIG has calved
Post by: AbruptSLR on February 17, 2014, 06:12:35 PM
I am concerned some readers will think that the influence of any El Nino event (possibly in the 2014-2015 austral summer) on the ASE marine glaciers and pinned ice shelves (i.e. PIIS, and Thwaites) is primarily due to the temporary increase in the volume of warm CDW conveyed into the ASE, and that due to the relatively slow rate of sub-ice-shelf melting from an incremental increase in CDW volume, that this effect would be relatively small and short-lived.  However, due to the interaction between an El Nino event and the ABSL (see following discussion of the ABSL), an El Nino event can also temporarily (multiple months, particularly from October to February) increase sea level in the ASE; which can: (a) reduce the pinning action of pinnacles; and (b) release pressurized subglacial hydrological basal water that previously had been sealed by the weight of the ice overburden at the marine glacial gateways (e.g. PIG and Thwaites); which can in-turn accelerate ice flow velocities from the marine glaciers (which could cause the residual Thwaites Ice Tongue to surge, which might shift, or displace, the pinned Thwaites Ice Tongue iceberg, discussed in my prior posts in this thread).

The following quote  is from the link after the quote, gives an idea about the importance of the ABSL and the ENSO/SAM cycles to the stability of the marine glaciers and pinned ice shelves in the ASE (I recommend going to the linked website about the ABSL and looking at the whole write-up and the various PowerPoint presentations there):

"Given these relationships, a main suspected factor from an atmospheric standpoint causing the temperature and sea ice changes described above are variations in the strength and position of the ABSL. Fundamentally, the ABSL exists because the Antarctic Peninsula and the off-axis nature of the Antarctic topography dynamically influence the atmospheric flow of the region (Baines and Fraedrich 1989; Lachlan-Cope et al. 2001). Its strength is influenced by large-scale patterns of climate variability that impact Antarctica, namely the Southern Annular Mode (SAM) and the El Niño - Southern Oscillation (ENSO). The SAM describes the strength of the mid-to-high latitude meridional pressure gradient and circumpolar zonal winds (Thompson and Wallace 2000; Marshall 2003). Although ENSO is a tropical climate oscillation, it impacts the whole globe through teleconnections. Its impact near Antarctica is in the region of the ABSL, part of an alternating wave-train of pressure/height anomalies stemming from the Tropics during ENSO events, known as the Pacific South American pattern (Karoly 1989; Mo and Ghil 1987; Renwick and Revell 1999; Mo and Paegle, 2001; Turner 2004; Yuan 2004; Lachlan-Cope and Connolley 2006)."

http://www.scalialab.com/absl/site/about.shtml (http://www.scalialab.com/absl/site/about.shtml)


The attached image (from the following link) showing how the ABSL drives wind and associate ocean surface currents towards the ASE, which not only drives warm CDW into the ASE, but also increase sea level within the ASE which serves to destabilize the marine glaciers and the pinned ice shelves in the ASE

http://www.scalialab.com/absl/site/presentationsFiles/zbacnik_AMS_ozone.pdf (http://www.scalialab.com/absl/site/presentationsFiles/zbacnik_AMS_ozone.pdf)

The following website discusses how telecommunication from the Pacific South American, PSA, pattern conveys energy to the Amundsen and Bellingshausen Sea areas (including the ASE):

http://www.sheffield.ac.uk/geography/phd/projects/teleconnection (http://www.sheffield.ac.uk/geography/phd/projects/teleconnection)



Title: Re: PIG has calved
Post by: AbruptSLR on February 17, 2014, 06:39:04 PM
I am making this post to acknowledge that the Antarctic sea ice melt season approaching its annual minimum (see the first attached image of the SH The Cryosphere Today SIA for Feb 16 2014, and the second image of the University of Bremen sea ice extent concentrations in the ASE for Feb 16 2014).  Therefore, I have enlarged the photo areas for the third and fourth attached images from Feb 17 2014 - Aqua, of the PIIS and Thwaites, areas respectively, in order to show that while some landfast sea ice is continuing to break-off (break-up), there are also signs of some areas of re-freezing of sea ice.
Title: Re: PIG has calved
Post by: AbruptSLR on February 18, 2014, 03:58:16 AM
While I am sure that Wipneus can do a much better job, I present the attached four Landsat images of cracks in the Southwest corner of the PIIS (near the junction with the SW Tributary).  From first to fourth, the images are from: Dec 6 2013, Dec 29 2013, Feb 8 2014 and Feb 17 2014; and I believe that these images show that the crack pattern is slowly growing and in particular, the crack appear to becoming slowly wider.  I imagine that at some point some significant areas of ice will calve from this area:
Title: Re: PIG has calved
Post by: AbruptSLR on February 18, 2014, 04:50:08 PM
The attached Landsat image is from Dec 6 2013 and indicates some recent (shortly before Dec 6th) calving in the notch area (as can be seen by looking a the images in reply 27 on Nov 26 2013 and in reply 30 on Dec 9 2013).  Also, note that in this image Block 2 is longer than more recent images show, indicating that Blocks 1 & 3 could be subjected to future calving depending on crevasse formation.
Title: Re: PIG has calved
Post by: Wipneus on February 23, 2014, 10:44:57 AM
Extending the animation with one scene:  Feb 19. The glacier ice moved in 9 days 3 pixels left, 4 down = 75m.

Sun elevation in the last scene is 18.1 degrees, down 3.0 degrees since Feb 10.

(don't forget to click the attached image)
Title: Re: PIG has calved
Post by: AbruptSLR on February 23, 2014, 05:07:59 PM
Wipneus,

It is great to see Feb 19 added to the sequence, and with the sun declining so quickly, it is unclear to me as to how much more, if any, fractured glacial ice will calve out of the notch area this austral summer.

However, I think that we should all remember that Favier et al. (2014), see reference at in of this post); have scientifically conservatively (omitting the influence of ocean-ice interaction and the influence of basal meltwater for both the glacier and the ice shelf, and the influence of the coming positive PDO cycle) projected that the speed of the PIG/PIIS ice stream will increase by a factor of five over the next twenty year, based on gravitation effects from the ice stream being unpinned from a ridge further upstream (further upstream than the pinnacle in the notch area).  Thus we can expect the PIIS ice stream to continue thinning, distorting and shearing at increasing rates in the future (winter & summer) regardless of what happens in the notch area.

Finally, I post a Feb 19 2014 Landsat 8 image of the cracking pattern in the PIIS near the SW tributary corner area, indicating to me that some of these cracks are shearing across the fracture plane, due to complex stresses in the ice in this local area.



http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2094.html (http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2094.html)

L. Favier, G. Durand, S. L. Cornford, G. H. Gudmundsson, O. Gagliardini, F. Gillet-Chaulet, T. Zwinger, A. J. Payne & A. M. Le Brocq, (2014) "Retreat of Pine Island Glacier controlled by marine ice-sheet instability", Nature Climate Change,  (2014); doi:10.1038/nclimate2094; 12 January 2014
Title: Re: PIG has calved
Post by: AbruptSLR on February 26, 2014, 04:54:23 PM
The attached three images from Landsat for Feb 24 2014, provide an update on the status of the notch area of PIIS, the SW Tributary corner of PIIS, and a portion of the Thwaites area, respectively.  These images some limited amount of recent calving and a few new cracks:
Title: Re: PIG has calved
Post by: AbruptSLR on March 01, 2014, 07:05:13 PM
The attached images of the Thwaites Ice Shelf/Residual Ice Tongue area are from Modis/Terra from the morning of March 1, 2014.  By comparing these two March 1 images with the Feb 24th Landsat image in my prior post, it is clear to see that while sea ice is starting grow in other parts of Antarctica, in the ASE the sea ice is still retreating; which is clearly freeing-up some of the berg-bit previously held by land-fast sea ice between the west side of the Thwaites Eastern Ice Shelf, and the grounded iceberg at the north end of the residual Thwaites Ice Tongue.  Also, the Southeastern base of the Thwaites Eastern Ice Shelf is showing more crevasse cracking now than on Feb 17 (see prior posts in this thread):
Title: Re: PIG has calved
Post by: AbruptSLR on March 02, 2014, 05:36:15 AM
As there still seems to be interest in this images, I am posting the attached Aqua images from the afternoon of March 1 2014, of the PIIS notch area (with some cloud cover), and of the Thwaites area, respectively.
Title: Re: PIG has calved
Post by: AbruptSLR on March 03, 2014, 01:16:27 AM
While there is cloud cover in these March 2 2014 Lance/Modis images of the PIIS and Thwaites, nevertheless, it is clear that in comparison with the March 1 2014 images: (a) in the first Aqua image some more fractures glacial ice has calved way from the eastern side of block 1 in the PIIS notch area; and (b) in the second and third attached Terra images show that there has been a significant amount of outward displacement of the bergy-bits previously trapped between the western side of the Thwaites Eastern Ice Shelf and the eastern side of the grounded iceberg at the end of the residual Thwaites Ice Tongue.  This indicates to me that there ocean water in the ASE is still relatively warm, and also probably that the wind is blowing northward.
Title: Re: PIG has calved
Post by: AbruptSLR on March 04, 2014, 01:42:19 AM
The attached March 3 2014 Terra image of the Thwaites area is much clearer than the March 2nd image:
Title: Re: PIG has calved
Post by: AbruptSLR on March 04, 2014, 07:16:25 PM
The attached Terra images from March 4, 2014 are the first clear images of both the PIIS and the Thwaites area, respectively.  The ice displacements are as I previously discussed.
Title: Re: PIG has calved
Post by: AbruptSLR on March 06, 2014, 12:31:03 AM
The first attached image of the PIIS notch area is from Aqua this morning (March 5, 2014), and shows no change from yesterday.

The second attached image is of the same area but from Terra several hours later on March 5 2014, but shows a large white field in the notch area.

The third attached image is of the same area but from Terra light contracted which indicates that the large white field in the notch area is not a cloud; therefore it must be: (a) an ice debris field (from a calving event), (b) snow blowing into the notch from the top of PIIS; or (c) newly frozen sea ice.

Subsequent images should clarify what this white field is.
Title: Re: PIG has calved
Post by: crandles on March 06, 2014, 02:42:18 AM
The first attached image of the PIIS notch area is from Aqua this morning (March 5, 2014), and shows no change from yesterday.

no change?

Is it me or does it look as if there is a lot less water in the notch? Has the glacier moved forward or is it something else?

Later terra image makes it look like the large block is nearer to hitting ice on the side.

Is that ice on the side going to be really weak or could impact? cause some blocks to dislodge from glacier?
Title: Re: PIG has calved
Post by: Wipneus on March 06, 2014, 09:55:32 AM
Also Landsat 8 was there, so I could add another frame to the sequence, March 5.

The glacier has moved about 5 pixels left, 7 down, about 130 meter since Feb 19.

(click that picture or no animation)
Title: Re: PIG has calved
Post by: AbruptSLR on March 06, 2014, 01:24:23 PM
Wipneus,

Thanks for adding the March 5 frame so quickly, as this image makes it very clear that the fractures glacier ice to the east of Block 1 calved, and knowing that the ice stream has moved 130m in two weeks gives us a good idea when Block 1 is going to run into the fractured glacial ice on the northern land-fast side of the PIIS.

crandles,

I have found that the Aqua image seems to suffer from some optical distortion, as the Landsat images makes it clear that the area of water in the notch is much larger than the March 5 Aqua image might otherwise indicate.

To respond to your question of the consequences of Block 1 eventually (in 2 of 3 months time) running into the northern land-fast side of the ice shelf: (a) the ice that Block 1 will impact is clearly fractured glacial ice and therefore is not a strong as an un-fractured ice shelf face, so I guess that it is weak but if this fractured ice gets pinned against the sound ice shelf face so that it can become compressed instead of sheared than it will put up much more resistance; (b) by the time Block 1 runs into the northern land-fast ice it will have moved off of the pinnacle so even if it becomes dislodged when it contacts the land-fast ice, that does not mean that the ice stream will necessarily accelerate; and (c) in 3 months time it will be relative dark in Antarctica so by then we may need to wait until m-d Sept. or early Oct. (depending on cloud cover at that time) to see what happened.
Title: Re: PIG has calved
Post by: AbruptSLR on March 06, 2014, 11:53:14 PM
The attached images for the PIIS and Thwaites are from Terra (afternoon) on March 6 2014.  You can see the recently calved area from the PIIS notch, but I do not see much change in the Thwaites area.
Title: Re: PIG has calved
Post by: AbruptSLR on March 08, 2014, 11:47:29 AM
The first image of the PIIS notch area is from Landsat on March 7 2014, and this image is what I would expect to see based on the Terra view from March 6 2014.

The second image of the PIIS is from Aqua for the morning of March 8 2014, and this image is not what I would expect to see and I am not sure what to say (optical distortion?, cloud? ice movement?)
Title: Re: PIG has calved
Post by: Andreas T on March 08, 2014, 02:11:36 PM
It is starting to get cold down there http://efdl_5.cims.nyu.edu/aws_pig/pig_env.html (http://efdl_5.cims.nyu.edu/aws_pig/pig_env.html)
with the low sun the shadows to the right in the picture identify high clouds, but lower fog and drifting snow would be hard to distinguish from snow covered ice. How soon before the (relatively) narrow notch gets an new ice cover?
Title: Re: PIG has calved
Post by: AbruptSLR on March 08, 2014, 06:05:41 PM
Andreas T,

I agree that at this time of year the atmosphere is getting colder, and there is a lot less solar radiance, and that one very likely explanation for the March 8 2014 Aqua image of the PIIS notch area is that sea ice is forming in portions of the notch; which might, or might not, has snow on top of such sea ice.  However, if the sea water advecting out from beneath the PIIS is warm enough, then it is also possible that the apparently new what material with the notch (on March 8 ) might also be newly calved fractured glacial ice from the shear zone extending East by Southeast from the notch.

The Terra image from the morning of March 8 are too cloudy to clarify this matter.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on March 09, 2014, 05:00:41 AM
While the attached Aqua image of the PIIS from the afternoon of March 8 2014 has cloud cover that partially obstructs the view; to me it looks like the notch area is slightly larger than on March 7 2014, possibly indicating that the Aqua image from this morning was showing an ice debris field in the notch from a possible calving event of previously fractured glacial ice from the shear zone between the ice stream and the land-fast ice shelf (it is also possible that Block 2 has shifted but the view is so poor that I cannot tell, but I think that it is a cloud that I see rather than shifted ice).
Title: Re: PIG has calved
Post by: AbruptSLR on March 09, 2014, 06:56:05 PM
The first attached image from Terra of the PIIS area for the morning of March 9 2014, shows that on March 8 2014 a major ice calving event happened on the land-fast section for fractured glacial ice (rather than for the fractured glacial ice to the East by Southeast side of the notch, nor has any shifting of Block 2 occurred) to the north side of the notch.  As this calved-ice-mass floats away, the notch will become larger.  Also, this image shows no signs of sea ice re-freezing.

The second attached image also from Terra of the Thwaites area for the morning of March 9 2014, shows little change within the past several days; however, this image also confirms that there is little, or no, re-freezing of sea ice in this area of the ASE.
Title: Re: PIG has calved
Post by: AbruptSLR on March 10, 2014, 04:05:49 AM
The first two images are from the Aqua afternoon imagining (some hours later than the Terra morning images in my immediately prior post) on March 9 2014, for the PIIS and Thwaites, respectively.  For comparison, I also provide a view of the PIIS from Landsat on March 5 2014.

With regards to the PIIS, in the Aqua image one can see that: (a) the calved fractured glacial ice masses (icebergs) are slowly moving away from the notch; and (b) I failed to previously note that the portion of the PIIS that I previously called the cracked area near the SW Tributary corner, also cracked-off on March 8 2014, forming a new iceberg.  Therefore, I speculate that the entire PIIS shock due to the cracking-off of the SW Tributary corner iceberg, which may have then induced the fractured land-fast glacial ice in the notch area to also calve-off (or the sequence of calving could be in the reverse order).

I provide the image of the Thwaites area for completeness, as I do not see much change from the Terra image this morning.
Title: Re: PIG has calved
Post by: sidd on March 10, 2014, 04:40:09 AM
Thanx for the pictures of the calving front. I am sorta interested in upstream views by the grounding line and even further up. I suspect something can be deduced from careful time lapse analysis of i ce surface elevation there. But that sounds like work, to which I am allergic. When i get to it in my copious spare time (ha!) i might try. This is related to VAF analysis, and my misgivings that seawater has got further upstream than we imagine. I shall try to find the time.

sidd
Title: Re: PIG has calved
Post by: AbruptSLR on March 10, 2014, 02:16:45 PM
sidd,

As we are both well aware Durand et al 2014 have projected that the contribution to SLR from PIG will increase by a factor of at least five within the next 20 years (due largely to traditional gravitational response); therefore, and VAF analysis (including rate of grounding line retreat) for PIG that you have time would be particularly interesting during this time of ice loss acceleration. 

If you do find time, then please open a new folder on this topic, as with the likely Super El Nino likely coming in 2014-15 (see the El Nino thread in the Consequence folder); it is probable that the acceleration in ice mass loss of five times in 20 years will be too low, due to both increase warming and particularly increase volume flow of CDW beneath the PIIS; which should activate more sub-ice-shelf basal melting; which should accelerate the "vertical" advection action beneath the PIIS; which I believe will lead to more "horizontal" advection of warm CDW from the PIG to the Thwaites Glacier; which should increase ice mass loss there.
Title: Re: PIG has calved
Post by: AbruptSLR on March 10, 2014, 10:19:22 PM
As today's Terra view has cloud cover, I decided to post this morning's images from Aqua for March 10, 2014, for the PIIS and Thwaites, respectively; even though the attached images look a little blurry and optically distorted to me.  Even though the PIIS image is distorted, one can see that both of the new fractured glacial ice icebergs have moved slightly from their locations from the March 9 2014 Aqua images.
Title: Re: PIG has calved
Post by: AbruptSLR on March 11, 2014, 05:51:38 PM
The first image is from Aqua on the afternoon of March 10 2014 and can be compared to the prior post from the morning of March 10.
The second image is from Terra on the morning of March 11 2014 and shows still more movement of the recently calves fractured icebergs.
The third image is from Terra on the morning of March 11 2014 and shows that simultaneous sea ice cracking/calving and sea ice formation are going on.
Title: Re: PIG has calved
Post by: AbruptSLR on March 12, 2014, 01:03:25 AM
I am just posting this March 11 2014 Aqua Afternoon image of PIIS because a portion of fragmented ice berg is floating away from the notch (as compared to this morning's image).
Title: Re: PIG has calved
Post by: AbruptSLR on March 13, 2014, 01:39:24 AM
The attached images from Terra on March 12 2014 for the PIIS, and Thwaites, respectively, are clear and self-explanatory:
Title: Re: PIG has calved
Post by: Wipneus on March 13, 2014, 08:38:14 AM
Indeed, fabulous clear weather on March 12. And to our luck, Landsat 8 was there as well.
Here a somewhat larger cut, at 30m resolution/8bits color to keep the file size small, for a wider view than I show in the animations.

Do click the picture for the full resolution image!

(animation will be updated later)
Title: Re: PIG has calved
Post by: Wipneus on March 13, 2014, 09:01:06 AM
Here is the animation (starts after a click).
I forgot to mention the sun elevation is 10.5 degress in that last frame.
Title: Re: PIG has calved
Post by: johnm33 on March 13, 2014, 10:28:51 AM
Great images thanks Wipneus
Title: Re: PIG has calved
Post by: Laurent on March 13, 2014, 11:16:28 AM
What is the width of what we are seeing ? 15 m/pixel but what is the pixel size?
Thanks a lot for your work all.
Title: Re: PIG has calved
Post by: Wipneus on March 13, 2014, 11:37:49 AM
What is the width of what we are seeing ? 15 m/pixel but what is the pixel size?
Thanks a lot for your work all.

It (the forum software)  shows below the picture its size:1068x855

Multiplying by 15 m, gives widthxheight: 16.020x12.825 (km x km)

(but perhaps I misunderstood your question)
Title: Re: PIG has calved
Post by: Laurent on March 13, 2014, 11:51:57 AM
You gave me the answer. I was more thinking of the size of the moving glacier but I have a good idea now, thanks.
Title: Re: PIG has calved
Post by: AbruptSLR on March 14, 2014, 06:46:57 PM
The attached image of PIIS is from Terra for March 14, 2014, and I believe that it shows some minor calving from the shear fractured glacial ice from the arm of the notch that points East by Southeast.
Title: Re: PIG has calved
Post by: AbruptSLR on March 14, 2014, 10:29:12 PM
The first attached image is from Landsat March 14 2014 focused on the notch area of the PIIS and it show that some sea ice re-freezing is occurring now with the notch.

The second image should be compared to the third image, both of the SW Tributary Corner of the PIIS, for March 14 and March 7 (with some cloud cover), 2014, respectively.  These images show the area of the shelf that formed an iceberg on March 12 2014.
Title: Re: PIG has calved
Post by: johnm33 on March 15, 2014, 01:00:17 PM
There's a great cloudless overview of the whole area [14th march]on https://earthdata.nasa.gov/labs/worldview/?map=-188462.556215,-57792,794577.443785,470592&products=baselayers,MODIS_Terra_CorrectedReflectance_TrueColor~overlays,arctic_graticule_3413,arctic_coastlines_3413&time=2013-09-03&switch=arctic (https://earthdata.nasa.gov/labs/worldview/?map=-188462.556215,-57792,794577.443785,470592&products=baselayers,MODIS_Terra_CorrectedReflectance_TrueColor~overlays,arctic_graticule_3413,arctic_coastlines_3413&time=2013-09-03&switch=arctic)   ,you'll have to navigate to antarctica and the date, but if I can anyone can.
 Better yet try, https://earthdata.nasa.gov/labs/worldview/?switch=antarctic&products=baselayers,MODIS_Terra_CorrectedReflectance_TrueColor~overlays,antarctic_coastlines&time=2014-03-14&map=-1790496,-390336,-1528096,-268224
Title: Re: PIG has calved
Post by: AbruptSLR on March 15, 2014, 10:02:01 PM
For those who want to use johnm33 route to worldview for Antarctica (instead the Arctic) it is better to use the following link:

https://earthdata.nasa.gov/labs/worldview/?map=-188462.556215,-57792,794577.443785,470592&products=baselayers,MODIS_Terra_CorrectedReflectance_TrueColor~overlays,arctic_graticule_3413,arctic_coastlines_3413&time=2013-09-03&switch=antarctic
Title: Re: PIG has calved
Post by: johnm33 on March 16, 2014, 01:40:03 PM
Thanks ASLR but we could both learn from JimHunt, check out his link on comment 45 of The 2014 Melting Season.
Title: Re: PIG has calved
Post by: AbruptSLR on March 17, 2014, 08:48:19 PM
The PIIS is covered with clouds today so I am posting this March 17 2014 Terra image of Thwaites to show that it looks like the re-freeze of local sea ice is starting to become more serious (at least around Thwaites).
Title: Re: PIG has calved
Post by: AbruptSLR on March 20, 2014, 06:26:17 PM
The attached March 19 2014 Landsat images of the PIIS and Thwaites, respectively, have a lot of cloud cover, but I am posting them anyway, as these may be some of the best images that we see for a will due to both increasing cloud cover and the increasing austral Fall darkness.
Title: Re: PIG has calved
Post by: AbruptSLR on March 21, 2014, 08:38:35 PM
As there is too much cloud cover to see anything today, I thought that I would post yesterday's (March 20 2014) somewhat cloudy Terra image of the PIIS showing little change from before.
Title: Re: PIG has calved
Post by: AbruptSLR on March 22, 2014, 01:03:05 AM
The clouds only revealed portions of Thwaites today, so the attached is an Aqua image for March 21 2014, which indicated very little change, with only a little new sea ice.
Title: Re: PIG has calved
Post by: AbruptSLR on March 26, 2014, 01:10:25 AM
Attached are images for the PIIS and Thwaites, respectively, from Terra for March 25, 2014; indicating that the sea ice refreeze is advancing.
Title: Re: PIG has calved
Post by: AbruptSLR on March 26, 2014, 09:57:05 PM
This Terra images of the PIIS are from March 26 2014 and they show that the local freezing of the sea ice is accelerating.
Title: Re: PIG has calved
Post by: AbruptSLR on March 30, 2014, 04:51:10 AM
The attached Aqua image of the PIIS for March 29 2014, indicates that there are areas of sea ice refreezing at the eastern end of the arm of the notch.
Title: Re: PIG has calved
Post by: AbruptSLR on April 02, 2014, 03:16:21 AM
Attached is an April 1 2014 Aqua image of Thwaites.
Title: Re: PIG has calved
Post by: AbruptSLR on April 12, 2014, 01:03:48 AM
The attached Terra image of the PIIS taken on April 11 2014 shows that the notch area is still not fully frozen in with sea ice, possibly due to the warming action of the advection of warm CDW.
Title: Re: PIG has calved
Post by: AbruptSLR on April 15, 2014, 01:01:24 AM
The attached Terra image for April 14 2014, only shows a portion of the PIIS; nevertheless it shows that sea ice still have not completely in-filled the notch; indicating that advection is keeping the SST in this limited area relatively warm.
Title: Re: PIG has calved
Post by: Wipneus on April 17, 2014, 07:14:10 AM
First images of the Sentinel-1A is released:

Acquired on 13 April 2014 at 09:03 GMT (11:03 CEST) this image covers parts of Pine Island Glacier  and Thwaites Glacier in West Antarctica. This image is among the first from Sentinel-1A, which was launched on 3 April. It was acquired in ‘Interferometric Wide Swath’ mode with a swath width of 250 km and in single polarisation. With Pine Island Glacier in a state of irreversible retreat, the Sentinel-1 mission is set to be an excellent tool for monitoring such glaciers as well as for providing timely information on many other aspects of the polar regions, such as sea ice and icebergs.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esa.int%2Fvar%2Fesa%2Fstorage%2Fimages%2Fesa_multimedia%2Fimages%2F2014%2F04%2Fpine_island_and_thwaites_glaciers_from_sentinel-1a%2F14475820-4-eng-GB%2FPine_Island_and_Thwaites_Glaciers_from_Sentinel-1A_node_full_image.jpg&hash=dc41bbe3d61b772c508e601cb804ba12)

Hi-res image here (http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2014/04/pine_island_and_thwaites_glaciers_from_sentinel-1a/14475821-4-eng-GB/Pine_Island_and_Thwaites_Glaciers_from_Sentinel-1A.jpg)

http://www.esa.int/spaceinimages/Images/2014/04/Pine_Island_and_Thwaites_Glaciers_from_Sentinel-1A (http://www.esa.int/spaceinimages/Images/2014/04/Pine_Island_and_Thwaites_Glaciers_from_Sentinel-1A)
Title: Re: PIG has calved
Post by: AbruptSLR on April 17, 2014, 10:42:09 PM
Wipneus,

Thank you for the excellent photo & link; however, when I look at the image I do not see any part of the Pine Island Ice Shelf, but I do see that the Thwaites Ice Shelf is continuing to shed bergy-bits; which indicates to me that advection is very strong in the ASE and that if we get a Super El Nino in 2014-15 we will like see a lot more calving events both for PIIS and Thwaites latter this year and next.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on April 17, 2014, 10:59:00 PM
Wipneus,

Your post about the Sentinel-1A image encouraged me to look back over the recent Terra & Aqua images of Thwaites for April and I found the two attached images.

The first attached image is from Terra for April 8 2014 and the second attached image is from Aqua for April 14 2014; both of which support the general condition of Thwaites indicated by the Sentinel-1A image.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on April 18, 2014, 12:26:30 AM
The following is a description of the Sentinel-1A satellite system:

"The first in the series, Sentinel-1, carries an advanced radar instrument to provide an all-weather, day-and-night supply of imagery of Earth’s surface.

The C-band Synthetic Aperture Radar (SAR) builds on ESA’s and Canada’s heritage SAR systems on ERS-1, ERS-2, Envisat and Radarsat.

As a constellation of two satellites orbiting 180° apart, the mission images the entire Earth every six days. As well as transmitting data to a number of ground stations around the world for rapid dissemination, Sentinel-1 also carries a laser to transmit data to the geostationary European Data Relay System for continual data delivery.

The mission will benefit numerous services. For example, services that relate to the monitoring of Arctic sea-ice extent, routine sea-ice mapping, surveillance of the marine environment, including oil-spill monitoring and ship detection for maritime security, monitoring land-surface for motion risks, mapping for forest, water and soil management and mapping to support humanitarian aid and crisis situations.

The design of Sentinel-1 with its focus on reliability, operational stability, global coverage and quick data delivery is expected to enable the development of new applications and meet the evolving needs of Copernicus."

per the following site:

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

Title: Re: PIG has calved
Post by: Wipneus on April 18, 2014, 01:12:29 PM
PIG Iceberg B31 is image-of-the-day of NASA's Earth Observatory.

Check out this link (http://earthobservatory.nasa.gov/IOTD/view.php?id=83519) for a nice overview, more images and video.

As of April 11, 2014, the U.S. National Ice Center (NIC) reported that B31 was 33 kilometers long and 20 kilometers wide (18 by 11 nautical miles). “While some mass was lost very early on in the life of B-31, it has remained pretty much the same shape since early December and is still about six times the size of Manhattan,” Bigg said. “Going on measurements of Pine Island glacier before the calving—and hints of partial grounding in the history of the iceberg movement—we think it is possibly 500 meters thick.”

NIC last observed B31 at 72° 23' South latitude, 108° 03' West longitude. Bigg added that “the iceberg is now well out of Pine Island Bay and will soon join the more general flow in the Southern Ocean, which could be east or west in this region.”


(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Feoimages.gsfc.nasa.gov%2Fimages%2Fimagerecords%2F83000%2F83519%2Fpig_amo_2014070.jpg&hash=cce23d6854006da4d79114ea913bdcf2)
Title: Re: PIG has calved
Post by: werther on April 18, 2014, 01:53:32 PM
That chunk is about as large as the average yearly mass loss of the GIS! A mighty ice-cream on the run.
Title: Re: PIG has calved
Post by: Jim Hunt on April 18, 2014, 06:42:11 PM
The following is a description of the Sentinel-1A satellite system

More on the Sentinel 1 thread (https://forum.arctic-sea-ice.net/index.php/topic,818), including news of a near collision with another satellite!
Title: Re: PIG has calved
Post by: AbruptSLR on April 23, 2014, 04:04:31 PM
The following link leads to a nice YouTube video about Ice Island (Iceberg) B31:

http://www.youtube.com/watch?feature=player_embedded&v=zwAOTvzrrFs# (http://www.youtube.com/watch?feature=player_embedded&v=zwAOTvzrrFs#)
Title: Re: PIG has calved
Post by: AbruptSLR on August 05, 2014, 08:31:04 PM
The attached Sentinel-1 image is also (see image in Reply #166) taken on April 13 2014, and it shows more detail about how fragmented the old Thwaites Ice Tongue (in Pine Island Bay) was on that date:
Title: Re: PIG has calved
Post by: nukefix on August 29, 2014, 06:26:42 PM
Arcuate crevasses on the trunk of PIG, Sentinel-1 dual-pol 23/08/2014. The scale of this thing is mind-boggling - the width of the scene is 70km!
Title: Re: PIG has calved
Post by: AbruptSLR on August 30, 2014, 02:07:04 AM
nukefix,

Thanks for the awesome image of the trunk of the PIG.  Do you have any idea how to locate this image relative to the calving face of the PIIS?

Best,
ASLR
Title: Re: PIG has calved
Post by: nukefix on August 30, 2014, 01:04:13 PM
The features are about 150km upstream of the calving face, I'm trying to make a full overview image but keep having some software glitches.
Title: Re: PIG has calved
Post by: nukefix on September 02, 2014, 10:51:11 AM
Here's the full view of the trunk, the features in the close-up are ~150km upstream from the calving front. I wonder how much snow&firn  is covering those crevasses..? (Please ignore the legend, the data is uncalibrated so the numbers are bunk.)
Title: Re: PIG has calved
Post by: AbruptSLR on September 02, 2014, 04:08:51 PM
nukefix,

Thanks for putting these images into context.  When those crevasses (covered with snow, or not) reach the caving face, it would seem believable that the PIG could loses its ice shelf, in much the same way as the Jakobshavn Glacier has lost its ice shelf.  It will be interesting to watch in the coming years.

Best,
ASLR
Title: Re: PIG has calved
Post by: nukefix on September 02, 2014, 05:15:14 PM
I believe it's normal to have crevasses at that area of the trunk, so business as usual. Here's a full-resolution zoom to show detail of the features (legend is bunk again). The crevasses are covered with snow and firn, I'll try to check how deep under the surface they are.
Title: Re: PIG has calved
Post by: NeilT on September 04, 2014, 10:04:02 PM
Isn't it the case that the PIG meets a small hill/mountain just before it flows out into the sea?  Could it be that which is causing the Crevasses?

I know that the sheet is melting underneath and towards this rise, but I was not aware of whether it had reached it or not.  I couldn't see the sheet losing enough mass until there was sufficient melt and lubrication to get it over the rise which is blocking the loss of ice.  Even so discharge has amplified simply with the shelf breakup.
Title: Re: PIG has calved
Post by: AbruptSLR on September 05, 2014, 12:30:09 AM
NeilT,

As the crevasses that nukefix is showing are located about 150 km upstream from the calving face, it is not possible that these crevasses are related to the rise that is currently helping to pin the Pine Island Ice Shelf, PIIS.  Crevasses occur naturally in ice streams; however, the number and extent of the crevasses in PIG are probably increasing as the velocity of the ice increases. 

My concern is that as the PIIS thins (due to basal melting), it will come unpinned from the rise (pinnacle), and then after some years (or decades) the PIIS could break-up; which would cause calving of PIG at the grounding line, along the crevasses in the ice stream, as currently occurs at Jakobshavn.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on September 16, 2014, 12:48:23 AM
The attached Terra image for Sept 15 2014 shows a portion of the PIIS; indicating that advection is keeping the SST in this limited area relatively warm, and that the notch is comparable (or larger) in size to what it was in late March, early April, 2014:
Title: Re: PIG has calved
Post by: AbruptSLR on September 16, 2014, 12:56:06 AM
Attached is the first Landsat8 image for Sept 15 2014 for the PIIS, confirming the Terra image in my previous post:

edit: I am providing the enlarged second image, but apparently there still is not enough sunlight to fully utilize the Landsat8's greater resolution (than Terra/Aqua).
Title: Re: PIG has calved
Post by: Wipneus on September 19, 2014, 08:32:39 AM
Here is an animation of the Sep 15 Landsat 8 image and one taken from the same orbital position on Feb 19.
The quality of the first image is indeed not so good, sun elevation is only 5.4 degrees, but the common features are easily visible.
I measure a distance of 2125m between the two images, which translates to an average speed of 10.2 m/day. That is slightly larger than the speeds during last summer season.

(resolution reduced to 60m to reduce the image size )

(needs a click to animate)
Title: Re: PIG has calved
Post by: AbruptSLR on September 19, 2014, 04:53:23 PM
Wipneus,

Thanks for the great animation, which in addition to indicating that the PIIS flow velocity has slight increased from the last austral summer to the current austral Winter/Early-Spring, also indicates to me that:

1. The PIIS face (and in particular the notch area) is currently actively calving (as the floating icebergs  clearly just recently calved).
2. The PIIS face is distorting both due to shear and rotational ice strain (particularly in the notch area).
3.  I suspect that basal ice melting in the notch area is making the pinning action of the local pinnacle less effective; which should lead to accelerating future ice flow rates, and accelerated ice calving event.

Furthermore, when you compare your Landsat8 image from Sept 15, with the attached Terra images from Sept 17 and 18, respectively, you can see that a local calving event in the Southwest corner of the PIIS face, leaves a small local notch in that Southwest corner visible in the Sept 18 image.

Best,
ASLR

edit: Note that north is to the left of these images.
Title: Re: PIG has calved
Post by: AbruptSLR on September 19, 2014, 06:02:08 PM
Just to elaborate on my point that a significant calving event happened in the notch area before Sept 15 (probably around Sept 11 or 12), attached is an Aqua image from Sept 9 2014 showing that the area just Southwest of the large notch had not calved yet but by Sept 15, it had clearly calved.
Title: Re: PIG has calved
Post by: AbruptSLR on September 19, 2014, 08:21:08 PM
The attached Aqua image of the PIIS from Sept 13 2014, shows the icebergs shortly after they calved on either Sept 11 or 12 2014:
Title: Re: PIG has calved
Post by: AbruptSLR on September 21, 2014, 04:26:08 PM
While Wipneus seems to be able to download higher resolution Landsat 8 images than I seem to be doing; nevertheless, I attach the accompanying Landsat 8 image of the PIIS taken on Sept 20 2014; which shows no new calving activity after Sept 17 2014:
Title: Re: PIG has calved
Post by: AbruptSLR on September 22, 2014, 01:33:56 AM
I am posting the blue-tinted Aqua image of PIIS from Sept 21 2014 in order to help see though the clouds; and while I might be wrong, it looks to me like calving is occurring in the Southwest corner of the PIIS (near the SW Tributary Glacier):
Title: Re: PIG has calved
Post by: AbruptSLR on September 22, 2014, 06:07:28 PM
The attached Aqua image from the late afternoon of Sept 21 2014, indicates that if any calving occurred in the southwest portion of the PIIS, then it must have been relatively minor.
Title: Re: PIG has calved
Post by: AbruptSLR on September 24, 2014, 08:13:13 PM
Here is today's Terra PIIA image showing little, or no, calving activity since my last post:
Title: Re: PIG has calved
Post by: AbruptSLR on September 24, 2014, 11:50:18 PM
I thought that the two attached images from Terra for the afternoon of Sept 24 2014, as:
(a) the first image of PIIS is clearer than this morning's image; and (b) the image of Thwaites is the first clear image of the current melt season and shows that the sea ice is already beginning to crack-up near Thwaites.
Title: Re: PIG has calved
Post by: AbruptSLR on September 28, 2014, 04:16:18 AM
Attached is the Aqua image of the PIIS for Sept 27 2014, showing little change from the Sept 24 2014 image; however, I am still concerned that the Southwest corner of the PIIS may degrade as the melting season progresses.
Title: Re: PIG has calved
Post by: AbruptSLR on September 30, 2014, 08:45:58 PM
I think that to get higher resolution Landsat 8 image, Wipneus orders larger files, but as I am too lazy to do that, I attach the Landsat 8 image for Sept 29 2014 at the resolution that can be downloaded from their website.  In any event, this image indicates almost no change to the PIIS calving face.
Title: Re: PIG has calved
Post by: AbruptSLR on October 03, 2014, 12:43:46 AM
The attached Terra image of Thwaites for Oct 2 2014 show that there has not been much change in the surrounding sea ice since the Sept 24 2014 images shown in Reply #193:
Title: Re: PIG has calved
Post by: AbruptSLR on October 12, 2014, 01:01:31 AM
As a follow-up to Reply #196, the attached image of the Thwaites Ice Shelf area taken by Terra on Oct 11 2014, shows that the degradation of the sea ice in this area is beginning to accelerate:
Title: Re: PIG has calved
Post by: AbruptSLR on October 20, 2014, 07:22:51 PM
While it has been cloudy in the ASE for over three weeks, which likely means that it has been snowing in this area.  Nevertheless, the attached Terra image of the PIIS for Oct 20 2014 clearly shows recent calving activity in the notch (in the northeast end of the ice shelf face); which to me indicates that the advection of warm CDW is continuing to cause basal ice melting in the PIIS.
Title: Re: PIG has calved
Post by: AbruptSLR on October 21, 2014, 05:41:55 PM
The attached Terra image of the PIIS taken today (Oct 21 2014), shows even more calving in the notch area than yesterday:
Title: Re: PIG has calved
Post by: Wipneus on October 23, 2014, 12:05:59 PM
Sentinel-1A image of the "notch" composed from the free user data (see Arctic Sea Ice thread "Sentinel-1 C-band data over Arctic sea ice starting to be available").
Until now it is the only image available (of the notch). I trimmed and decreased the resolution from 25m10m to 100m40m to keep the file size normal (it is from a 850MB zipped download), but you get the idea what is possible.
On the right side there is, what looks like a huge crack and a possible new giant calving.

EDIT: the resolution of the original appeared to be 10m.
 
Title: Re: PIG has calved
Post by: Lennart van der Linde on October 23, 2014, 06:43:50 PM
Wipneus, thanks. How many pixels/km from that huge crack to the sea?
Title: Re: PIG has calved
Post by: Wipneus on October 24, 2014, 06:55:51 AM
Wipneus, thanks. How many pixels/km from that huge crack to the sea?

Lennart, the pixel size in that image is 40m. Just counting from the middle of the crack to an imaginary calving line gives about 18km distance.
Title: Re: PIG has calved
Post by: Wipneus on October 24, 2014, 08:19:30 AM
Here is a detail of the "crack" in a Sentinel-1 image from October 22, resolution is 10m/pix so the crack width is 40-60m wide.
It is currently too cloudy to see it on Landsat images.
Orientation is due to the different position of the satellite, this is in the ascending part of the orbit where the previous image was taken from the descending position.


Title: Re: PIG has calved
Post by: AbruptSLR on October 25, 2014, 07:39:51 PM
Wipneus,

Thank you for your very enlightening posts about the recently observed major crevasse about 18km upstream from the approximate PIIS calving face.  This crevasse looks like it may have been caused by flexural bending, possibly because as the PIIS thins it is more subject to tidally induced bending.  It will be interesting to watch to see whether this crevasse contributes to a major calving event within the next several years, or if the situation is deteriorating fast enough, whether such a major calving event happens within the next year.

Best,
ASLR

edit: The attached Aqua image of the PIIS for Oct 25 2014, indicates that the "notch" is moving upstream relatively quickly (for this time of year); which makes me wonder what will happen if/when the notch, and the major crevasse, extend sufficiently to intersect.
Title: Re: PIG has calved
Post by: sidd on October 25, 2014, 09:46:22 PM
I think that notch is a flow characteristic, not a melt characteristic. The real action is below the shelf and at the base of grounding line, the deeper you go, the greater the differential between local freezing point  and CDW temperature, and the faster the melt rate. Anyone care to hazard a guess how far upstream and how deep the base at grounding line is this year ?

sidd
Title: Re: PIG has calved
Post by: AbruptSLR on October 25, 2014, 10:47:57 PM
sidd,

In Reply #185, Wipneus provided the following post:
"Here is an animation of the Sep 15 Landsat 8 image and one taken from the same orbital position on Feb 19.
The quality of the first image is indeed not so good, sun elevation is only 5.4 degrees, but the common features are easily visible.
I measure a distance of 2125m between the two images, which translates to an average speed of 10.2 m/day. That is slightly larger than the speeds during last summer season."

Therefore, you are correct that the flow velocities are "slightly larger" than the last austral summer season; which is certainly is making some contribution to the growth of the notch.  However, basal melting is also important and the linked reference (with a free pdf) presents numerical model studies relating the oceanographic and geometric (of the cavity beneath the PIIS) controls on ice melting for the PIG (and PIIS).  They found that after an initial surge of ice melting after the 1970's with grounding line retreated past the well-known subglacial ridge; thereafter the melting rate was more dominated by the depth of the thermocline.  Remember that the depth of the thermocline is related to the ENSO cycle (via the ASL) and that as we enter a period of increasingly positive PDO, the depth of the thermocline should be increasingly conducive to accelerated rates of ice melting.

J. De Rydt, P.R. Holland, P. Dutrieux, and A. Jenkins, (2014), "Geometric and oceanographic controls on melting beneath Pine Island Glacier", Journal of Geophysical Research-Oceans, 119:2420-2438. doi: 10.1002/2013JC009513

http://www.antarctica.ac.uk/met/ph/docs/2014_DeRydt&Al_JGRO.pdf (http://www.antarctica.ac.uk/met/ph/docs/2014_DeRydt&Al_JGRO.pdf)

See also, the three attached images (that you have seen before) related to: (a) grounding line retreat and location, and (b) flexural bending of the PIIS.

Best,
ASLR
Title: Re: PIG has calved
Post by: icefest on October 26, 2014, 12:51:10 AM
I had a quick play with wipneus' image of the notch. I changed contrasts, noise and curves; hoping to get a tad more detail out of the image.

I couldn't help but notice that there seems to be a "bend" in the fracture line on the river right, moving from about 120° paralell to the direction of motion. While this could be an imaging artifact, it seems to make a new calving this summer less likely. I've madea copy and highlighted it in red.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FcqwNh%2F886dfa6fb2.jpg&hash=978ddd0b271c851ce7d470328bbd0171)

Here is plain edit, without my drawings: http://puu.sh/cqxb5/dd24c1b596.jpg (http://puu.sh/cqxb5/dd24c1b596.jpg)
Title: Re: PIG has calved
Post by: AbruptSLR on October 26, 2014, 03:59:15 PM
icefest,

Thanks for your analysis, and I must concur that a major calving event for the PIIS within a year from now (ie by the austral Spring of 2015, say through the end of November 2015) is not the most probable scenario, but in my opinion it is plausible for reasons including:
(a) The image the Wipneus posted, and that you analyzed, are from Oct 9 2014, while the image of the PIIS on Oct 25 2014 that I posted in Reply #204 shows just over two weeks the notch has extended noticeably and we are still a long way from the austral Summer of 2014-2015.
(b) Major cracks often bifurcate, so the "bend" that you point to does not mean that the main crack may not continue propagating on its primary alignment, or even bifurcate a branch bending toward the northwest.
(c) Shear cracks from near the tip of the notch could extend southward to intercept what I am calling the major flexural crevasse (or fracture line).  Furthermore, shear cracks from the small notch in the Southwest corner of the PIIS could propagate northeastward, also to intercept the major flexural crevasse.
(d) If an El Nino occurs between January 2015 and Nov 2015 (as NOAA is forecasting) then the advection of warm CDW into the Pine Island Bay shown increase, which would not only increase the basal ice melting for the PIIS, but also the water drag force on the bottom of the PIIS (remember that the last major calving for the PIIS occurred in July of 2013 and floated way from the calving face in November of 2013).

Also the following linked research shows that the basal melting for the PIIS is highly channelized the can promote the formation of localized crevasses:

http://www.scienceworldreport.com/articles/9456/20130913/warm-ocean-water-beneath-antarctic-glacier-melts-ice-unprecedented-rate.htm (http://www.scienceworldreport.com/articles/9456/20130913/warm-ocean-water-beneath-antarctic-glacier-melts-ice-unprecedented-rate.htm)
 
Best,
ASLR
Title: Re: PIG has calved
Post by: icefest on October 27, 2014, 01:10:04 AM
Thanks ASLR,

I very much agree with most of your analyses, and this one is no exception!

I'm not sure if this has been previously discussed, but do we have any detailed bed topology of the area of the notch? It seems that the start of the fractured crack (not where the water begins, but further up, where the glacier starts its massive deformation) doesn't move a huge amount with the years and seasons.

It'll be nice to have some clearer landsat 8 shots of the area. That would make it much easier to tell how the crack is progressing.
Title: Re: PIG has calved
Post by: AbruptSLR on October 27, 2014, 02:49:47 AM
icefest,

Attached is a fairly recent bed topological map beneath the PIIS (with the groundling line location from several years ago, circa 2009.  Note that Reply #206 shows an image with a more recent location for the PIG groundling line), which indicates a pinnacle near the upstream end of the notch, while the end of the peninsula maybe closer the point of the beginning of the heavy shear deformation upstream of the notch.

Best,
ASLR
Title: Re: PIG has calved
Post by: icefest on October 27, 2014, 03:35:03 AM
Thank for that ASLR,

I agree, I doubt it's that pinnacle, it's too far downstream.

Could it be the lateral compression as the glacier gets pushed to the river left, and then deforms back after passing the peninsula on the river right. That would mean that once calving progresses higher than the peninsula the notch would be less likely to form.
Title: Re: PIG has calved
Post by: AbruptSLR on October 27, 2014, 04:44:01 AM
icefest,

You might want to look back at Replies #20 and #33 to get a better idea of what might be happening in this dynamic portion of the PIIS.

Best,
ASLR
Title: Re: PIG has calved
Post by: icefest on October 27, 2014, 02:21:23 PM
ASLR,
Thanks for the reminder, it's been a while since I've read them.

The timelapse in #20  (http://forum.arctic-sea-ice.net/index.php/topic,429.0.html)represents quite clearly what I'm trying to say. The most upstream part of the rift, the origin, seems to stay in the same spot. Always right next to Evans Knoll.
As far as I can tell, Evans Knoll is the name of the visible nutatak closest to the glaciers calving face. I think it's also at the northern part of the same peninsula where PIG is grounded.

Even in post #33, the rift seems to be occurring at the same location. That was taken in 1973.

I agree that the rifted area is incredibly clear, and that this is a recent historical aberration, though I think the rifting has been present for a while.
-icefest
Title: Re: PIG has calved
Post by: AbruptSLR on October 27, 2014, 03:15:28 PM
icefest,

Attached is a Google Earth image of this area, that I guess shows Evans Knoll in its upper left-hand corner, which also shows the raised outline of the peninsula that Evans Knoll sits on.  This image does support you idea that upstream of the tip of the peninsula the shears ice zone is in compression, while downstream this compression is relieved, resulting in the rifting that feeds into the notch.

Other old replies that are good to review on this matter include:
- Reply #76 that shows the location of the pinnacle relative to the notch.
- The first image in Reply #89  that shows an old Landsat 7 image of a flexural crevasse linking to shear cracks in this general area.
- The third (& fourth) image(s) in Reply #93 that show the shear strain rates (and ice velocities) in the PIIS.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on October 27, 2014, 08:54:29 PM
The attached Terra image of the PIIS, is from Oct 27 2014, and indicates that there has been no significant calving in the past few days; however, it does show more fracturing (cracking) of the ice shelf upstream of the notch, and also in the smaller notch in the Southwest corner of the PIIS.
Title: Re: PIG has calved
Post by: AbruptSLR on October 27, 2014, 11:15:47 PM
The attached image from the Modis mosaic of Antarctica for Oct 27 2014, shows that the sea ice is continuing to retreat from the Amundsen Sea Embayment:
Title: Re: PIG has calved
Post by: icefest on October 28, 2014, 01:24:19 AM
Thanks for the support ASLR,  :)

Thinking more about the lateral compression, it seems that there is a compression from the opposite side, a bit further down. This pushed the calving face to the river right, after passing Evans Knoll.

I suspect, but can't prove, that this deformation force increases the backpressure on the rest of the glacier, as it forces the visible bend to the river right.

I suspect that this deformation was part of the reason the calving broke off the way it did (first the river right, the the river left last, as it was in compression for the longest). I think this may be a protective factor, decreasing the chance of a large calving soon. I hope.

I worry about the rate of decline once the calving front passes those lateral pinning points.  That's when it'll really start flying. :(

EDIT: Forgot to add image:
A is the compression force due to Evans Knoll, B is the one on the opposite, causing the flexion around Evans Knoll.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FctqC0%2Fa3a4a19f14.jpg&hash=1cb6105d799c5459e4ee160d4b62517d)
Image from ASLR (http://forum.arctic-sea-ice.net/index.php/topic,429.msg20014.html#msg20014)
Title: Re: PIG has calved
Post by: icefest on October 28, 2014, 01:32:47 AM
If there is a deflection and compression like this, you would expect the crevice in the previous image to cease to line up as attached ice deformed and the free floating didn't . I'm not sure if the imagery from them is up to it.
Title: Re: PIG has calved
Post by: AbruptSLR on October 28, 2014, 02:46:28 AM
If there is a deflection and compression like this, you would expect the crevice in the previous image to cease to line up as attached ice deformed and the free floating didn't . I'm not sure if the imagery from them is up to it.

icefest,

I agree with almost everything that you say (your English is a little rough though); however, I am particularly tired (and distracted) at the moment, so I will say a few things now and I will try help more later:
1,  I suggest that you read my Reply #51, as the location of the initial flexural crack has been migrating upstream (the 2013 calving that first formed in 2011 was the furthest upstream every observed), and I believe that this is related to both the thinning of the ice shelf, and the basal drag, associate with the advection of warm CDW.
2. You seem to have neglected that the compression force near the point B (on the left bank of the descending ice stream) is associated with the outflow of the Southwest (SW) Tributary glacier (coming from the Thwaites Basin, see the discussion in the PIG/Thwaites 2012 to 2040/2060 thread).  This actively loads the PIIS like 1/2 of a deep-beam with the compressive reaction near the point that you label A (there are many books on deep-beam action that show the cracking pattern that we are discussing, if you Google the topic (or use Google books)).
3.  You also appear to be neglecting the influence of the ENSO cycle on the temperature of the ocean water at the base of the ice shelf, as this temperature can influence the melting or formation of ice (that can heal) in the bottom portion of the crevasse.
4.  The thread about the FRIS/RIS ice shelves contains references about the formation and propagation of crevasses in these flowing ice streams.

My concern is that a Super El Nino could occur by next October (2015) that if combined with the influence of the Amundsen Sea Low, ASL, could induce stresses in the PIIS by the end of next November (2015) that it is plausible that a major calving could occur in 2015 rather than a few years from now.  I am also concerned that if a major calving occurs sufficiently far upstream then the SW Tributary Glacier will be "uncorked", which will: (a) relieve the compression stress reacting near the point that you label A, thus causing the PIG to accelerate, and (b) will trigger the eastern shear zone of the Thwaites ice stream causing Thwaites to accelerate.

Goodnight,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on October 28, 2014, 04:18:18 PM
icefest,

Due to distractions, the following is all that I can provide in support of your theory of the current major calving risk (crack pattern) for the PIIS.

First, the first attached image shows the cracking pattern in a concrete deep beam.  If you consider only the right half of this beam, the stress patterns have some degree of relevance to the stress/cracking patterns of the PIIS associated with its risk of a potential major calving in the near future.

Second, regarding the SW Tributary Glacier (that feeds into the PIIS), the linked reference (with a free pdf and see the second attached reference figure) presents a very interesting discussion:

http://www.igsoc.org/journal/59/217/j13J050.pdf (http://www.igsoc.org/journal/59/217/j13J050.pdf)


Weak bed control of the eastern shear margin of Thwaites Glacier, West Antarctica; Joseph A. MacGREGOR, Ginny A. CATANIA, Howard CONWAY, Dustin M. SCHROEDER, Ian JOUGHIN, Duncan A. YOUNG, Scott D. KEMPF, & Donald D. BLANKENSHIP; Journal of Glaciology, Vol. 59, No. 217, 2013 doi: 10.3189/2013JoG13J050

Third, the two following references (including Bassis as a co-author) are related to cracking in ice shelves:

Heeszel, D. S., H. A. Fricker, J. N. Bassis, S. O'Neel, and F. Walter (2014), Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure, J. Geophys. Res. Earth Surf., 119, 731–744, doi:10.1002/2013JF002849.

http://onlinelibrary.wiley.com/doi/10.1002/2013JF002849/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013JF002849/abstract)

Abstract: "Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important process involved in calving is the initiation and propagation of through-penetrating fractures called rifts; however, the mechanisms controlling rift propagation remain poorly understood. To investigate the mechanics of ice shelf rifting, we analyzed seismicity associated with a propagating rift tip on the Amery Ice Shelf, using data collected during the austral summers of 2004–2007. We apply a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show ice shelf rifting is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h. Even during periods of quiescence, we find significant deformation around the rift tip. Moment tensors, calculated for a subset of the largest icequakes (Mw > −2.0) located near the rift tip, show steeply dipping fault planes, horizontal or shallowly plunging stress orientations, and often have a significant volumetric component. They also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf. This suggests a complex system of deformation that involves the propagating rift, the region behind the rift tip, and a system of rift-transverse crevasses. Small-scale variations in the mechanical structure of the ice shelf, especially rift-transverse crevasses and accreted marine ice, play an important role in modulating the rate and location of seismicity associated with the propagating ice shelf rifts."



C. C. Walker, J. N. Bassis, H. A. Fricker, and R. J. Czerwinski, (2013), "Structural and environmental controls on Antarctic ice shelf rift propagation inferred from satellite monitoring", Journal of Geophysical Research: Earth Surface, Volume 118, Issue 4, pages 2354–2364, DOI: 10.1002/2013JF002742.


http://onlinelibrary.wiley.com/doi/10.1002/2013JF002742/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013JF002742/abstract)


Abstract: "Iceberg calving from ice shelves accounts for nearly half of the mass loss from the Antarctic Ice Sheet, yet our understanding of this process is limited. The precursor to iceberg calving is large through-cutting fractures, called “rifts,” that can propagate for decades after they have initiated until they become iceberg detachment boundaries. To improve our knowledge of rift propagation, we monitored the lengths of 78 rifts in 13 Antarctic ice shelves using satellite imagery from the Moderate Resolution Imaging Spectroradiometer and Multiangle Imaging Spectroradiometer between 2002 and 2012. This data set allowed us to monitor trends in rift propagation over the past decade and test if variation in trends is controlled by variable environmental forcings. We found that 43 of the 78 rifts were dormant, i.e., propagated less than 500 m over the observational interval. We found only seven rifts propagated continuously throughout the decade. An additional eight rifts propagated for at least 2 years prior to arresting and remaining dormant for the rest of the decade, and 13 rifts exhibited isolated sudden bursts of propagation after 2 or more years of dormancy. Twelve of the fifteen active rifts were initiated at the ice shelf fronts, suggesting that front-initiated rifts are more active than across-flow rifts. Although we did not find a link between the observed variability in rift propagation rate and changes in atmospheric temperature or sea ice concentration correlated with, we did find a statistically significant correlation between the arrival of tsunamis and propagation of front-initiated rifts in eight ice shelves. This suggests a connection between ice shelf rift propagation and mechanical ocean interaction that needs to be better understood."

Fourth (and finally), the following summary research statement provide an idea of the ice shelf fracturing and flow pattern of the Filchner Ronne Ice Shelf from 2003 to 2004 field data, which has some moderate relevance to the PIIS situation:

Hulbe, C. L., and C. M LeDoux. 2011. MOA-derived Structural Feature Map of the Ronne Ice Shelf. [indicate subset used]. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5PR7SXR. (http://dx.doi.org/10.7265/N5PR7SXR.)
 
Summary statement:
"This data set provides a structural feature map of the Ronne Ice Shelf in Antarctica (also known as the Filchner-Ronne Ice Shelf). The map was developed as part of a project to study fracture propagation in the Ronne Ice Shelf, with special focus on the Evans Ice Stream. Features were digitized from the MODIS Mosaic of Antartica (MOA), a composite of individual Moderate Resolution Imaging Spectradiometer (MODIS) images taken between 20 November 2003 and 29 February 2004, with an effective resolution of 125 m. The data set includes estimates of the shelf boundary, including ice stream grounding zones, outlets of glaciers feeding the shelf, extents of islands and ice rises, and the location of the shelf front, and features observed within the shelf, including suture zones between ice streams, streaklines, fractures (crevasses and rifts), and fold-like features. Individual features can be extracted as a group of points and grouping is used to facilitate identification and plotting."

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on October 28, 2014, 04:35:44 PM
One last post for the moment.

The first attached image shows the PIIS cracking pattern on July 2013, which illustrates how the shear cracks on both edges of the ice stream and link-up with the flexural crack in the middle of the ice stream to create a calving face; however note that this calving face was initiated well downstream of the current major flexural crack identified by Wipneus, and in the second attached image I superimpose blue lines on top of your enhanced version of Wipneus's image to show how I imagine that a new major calving face could (plausibly but many not likely) develop upstream of where the SW Tributary Glacier feeds into the PIIS.
Title: Re: PIG has calved
Post by: AbruptSLR on October 28, 2014, 06:57:14 PM
As was discussed last austral summer, the notch would probably need to expand to the inner edge of the red curve shown on the attached edited image of Wipneus's photo, in order for a major calving to swing past the pinnacle within the next year.
Title: Re: PIG has calved
Post by: crandles on October 28, 2014, 11:52:39 PM
As was discussed last austral winter, the notch would probably need to expand to the inner edge of the red curse shown on the attached edited image of Wipneus's photo

aaaarrrrgggghhh don't put a curse on it.  ;)
Title: Re: PIG has calved
Post by: AbruptSLR on October 29, 2014, 12:26:16 AM
Thanks for the catch.  I have changed "red curse" to "red curve"
Title: Re: PIG has calved
Post by: AbruptSLR on October 29, 2014, 03:23:13 PM
I am providing this post to clarify my discussion about comparing the major calving crack-inducing stress fields in the PIIS to one half of a deep concrete beam.  In that analogy what is important is the bottle-shaped compressive field between the loading point (the outlet of the SW Tributary Glacier, or point B in icefest's post) and the reaction point (the peninsula with Evans Knoll, or point A in icefest's post, in Reply #217).  The two attached figures are from the linked Arabzadeh et al (2012) article about compressive and tensile stress fields in bottle-shaped struts.  The first attached image shows how geometry can affect the dispersion of compressive and tensile stresses within the bottle-shaped strut.  These stress dispersion patterns are capable of producing the long tensile fields along the centerline of the strut that can produce what I have called the "flexural crack" (that are likely triggered by out-of-plane tidally induced flexural tension due to cantilever action of the entire ice shelf), as shown in the second attached image for cases both before and after cracking.

A. Arabzadeh, R. Aghayari, A. R. Rahai, (2012), "A new model for predicting the effective strength in reinforced concrete bottle-shaped struts", International Journal of Civil Engineering, Vol. 10, No. 4, December 2012

http://ijce.iust.ac.ir/files/site1/user_files_6k93w6/eng/arabzade.a-A-10-574-2-548b91231.pdf (http://ijce.iust.ac.ir/files/site1/user_files_6k93w6/eng/arabzade.a-A-10-574-2-548b91231.pdf)
Title: Re: PIG has calved
Post by: AbruptSLR on October 29, 2014, 06:46:28 PM
As a follow-up to my post in Reply #225, obvious the stress distribution shown for the bottle-shaped strut only accounts for the flexural/tension crack shown in Wipneus's image; which does not form a failure surface to support a major calving event.  As previously stated, I believe that the shear cracks on both the left and right banks of the ice stream in the PIIS will grow with time (as the ice flows towards the ocean) until they intersect the primary flexural/tensile crack.  Obviously. due to the inflow of ice from the SW Tributary Glacier the shear cracking in the southwest corner of the PIIS ice stream (ie the left bank) must occur downstream of the SW Tributary Glacier, and thus this section fails last.  However, on the right bank of the ice stream, near the upstream tip of the notch, the shear in this area comes from the restraint of the pinnacle, so the shear deformations are much larger here (because the restraint from the pinnacle is much less than from the SW Tributary Glacier) thus this shear crack typically grows more rapidly; & when it intersects the main flexural/tensile crack, it forms a rotational mechanism that allows the new ice berg to rotate counter-clockwise about the southwest corner, once the restraint from the pinnacle is relieved due to lock minor calving.

The attached Aqua image of the PIIS for Oct 28 2014, clearly shows the growth of shear cracks in both the upstream end of the notch, and in the southwest corner of the PIIS ice stream (downstream of the SW Tributary Glacier), which I will call the minor notch.  This relatively rapid formation of cracks that may form a failure mechanism for a major calving event, confirms that it is plausible that such a major calving could happen by the end of the austral Spring of 2015.
Title: Re: PIG has calved
Post by: AbruptSLR on November 03, 2014, 10:23:26 PM
The attached Terra image of PIIS taken on Nov. 3 2014 indicates that the notch extends further upstream (as compared to the Oct 29 image in the last post); and thus is moving closer to connecting with the major flexural crack.
Title: Re: PIG has calved
Post by: Wipneus on November 04, 2014, 07:23:56 PM
Esa is filling the Sentinel archives in a, to me, unpredictable way. Yesterday I noticed the first "Single Look Complex" (SLC) data file of the area of interest. Date is October 21.
This has an even higher resolution than the "Ground Range Detected" (GRD) images that I posted before. In this case the meta data indicates 2.3m in the data range direction and 14m in azimuth.
That enables us to have a better look at the width of "the crack" which is running nicely perpendicular to the satellite track.
From this image I guess the width is a bit less than 50m.

Click the image for full resolution ( which is different in x and y directions).
Title: Re: PIG has calved
Post by: Wipneus on November 05, 2014, 12:30:11 PM
Of course it is more fun as an animation. Here is a sequence between October 21 and November 2, 12 days is the repeat period of the Sentinel-1A satellite.

(click to animate)
Title: Re: PIG has calved
Post by: AbruptSLR on November 06, 2014, 11:12:39 PM
It is informative to compare the current PIIS major crevasse that Wipneus identifies as being about 50m wide (and growing) with the two attached images of the immediate prior major crevasse that was about 80m wide when it was identified in October 2011 (see the first image and caption and link).  The second image (from the second link) shows a reflectance image of that prior major crevasse on January 1 2012.  Note that the iceberg associated with the prior major crevasse calved in July 2012 and floated away in November 2012, and it is interesting to consider that the current major crevasse might progress to a comparable calving event in a similar timeframe (ie calving within one year of its identification).

http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=10860 (http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=10860)
Caption for first image: "The torch of the Statue of Liberty would not quite peek out of the deepest points of the crevasse currently opening up across the Pine Island Glacier ice shelf in Antarctica. This image is based on data from the Airborne Topographic Mapper (ATM), which flew over the rift on NASA's DC-8 on Oct. 26, 2011. The scale at the bottom was taken from one of the rift's widest single points. For much of the line the DC-8 flew over, the crevasse was about 80 meters wide, but it is constantly changing."

http://icyseas.org/tag/antarctica/ (http://icyseas.org/tag/antarctica/)
Caption for second image: "Pine Island Glacier and Bay, Antarctica on Jan.-1, 2012 as seen by MODIS Terra, notice the whitish crack near the center of the image.
Title: Re: PIG has calved
Post by: AbruptSLR on November 09, 2014, 12:52:09 AM
The attached Landsat 8 image of the PIIS for Nov 7 2014 is not of much better quality than the Terra images as I downloaded it from the internet.  If Wipneus were to order this image, it would likely show higher resolutions.
Title: Re: PIG has calved
Post by: Jim Hunt on November 09, 2014, 03:24:41 AM
The attached Landsat 8 image of the PIIS for Nov 7 2014 is not of much better quality than the Terra images as I downloaded it from the internet..

You've got me confused ASLR? Here's an extract from the "Natural Color" image. All I did was download it from EarthExplorer and crop it:

Title: Re: PIG has calved
Post by: Wipneus on November 09, 2014, 08:06:18 AM
If Wipneus were to order this image, it would likely show higher resolutions.

I will surely try! For now someone has to fix this:

EarthExplorer Unavailable - System Error
EarthExplorer has encountered an unexpected error. Please try again later.

EDIT: never mind, it works again. Downloading 909MB now.
Title: Re: PIG has calved
Post by: Wipneus on November 09, 2014, 09:42:51 AM
ASLR, here is an image produced by the following steps:
- download the zipped geo-TIFF file (909MB)
- unpack
- load the *_B8.TIFF file into the Gimp. This is a panchromatic (B&W) image at the highest resolution (15m and 12 significant bits per pixel);
- Cut the relevant part using the square selection tool and select image->cut to selection;
- Improve the contrast using colors->automatic->equalize;
- reduce the resolution (using image->scale) to get the filesize to something managable;

I will let the image (30m resolution) speak for itself.

(click to see the 2MB image)
Title: Re: PIG has calved
Post by: Wipneus on November 09, 2014, 09:55:11 AM
An here a closeup (15m pixels) of the crack. In the visual, it is much wider than in those from the Sentinel-1's radar. It is at least 100m at its widest.
Title: Re: PIG has calved
Post by: Espen on November 09, 2014, 10:38:01 AM
It looks like the crack will expand further between the red lines?

Title: Re: PIG has calved
Post by: AbruptSLR on November 09, 2014, 11:22:08 AM
ASLR, here is an image produced by the following steps:
- download the zipped geo-TIFF file (909MB)
- unpack
- load the *_B8.TIFF file into the Gimp. This is a panchromatic (B&W) image at the highest resolution (15m and 12 significant bits per pixel);
- Cut the relevant part using the square selection tool and select image->cut to selection;
- Improve the contrast using colors->automatic->equalize;
- reduce the resolution (using image->scale) to get the filesize to something managable;

I will let the image (30m resolution) speak for itself.

(click to see the 2MB image)

Wipneus,
Thank you very much (I don't think I am entitled to a USGS account with download privileges for the geo-TIFF files) for the spectacular image.  Here is a natural light cropped image of the Southwest corner of the PIIS indicating a strong likelihood of local calving in this area in the next few months. 
Best,
ASLR
Title: Re: PIG has calved
Post by: Jim Hunt on November 09, 2014, 02:39:33 PM
(I don't think I am entitled to a USGS account with download privileges for the geo-TIFF files)

Have you tried registering for Earth Explorer? I managed it without any problem, and I'm not "affiliated" to any particular "organisation". It looks like you can now get the JPGs OK at least?
Title: Re: PIG has calved
Post by: Wipneus on November 09, 2014, 03:43:25 PM
That is what I remember as well. If there is nothing appropriate in the list of choices there is usually "other" for which I usually enter "home", or "private" or even "hobby".
Title: Re: PIG has calved
Post by: Hunter on November 09, 2014, 09:35:12 PM
I think these are pics of the new crack, taken Oct 29th 2014

credit to NASA

First pic is the calving front, just because I know you all like to check it out :)
Title: Re: PIG has calved
Post by: AbruptSLR on November 10, 2014, 02:50:17 AM
(I don't think I am entitled to a USGS account with download privileges for the geo-TIFF files)

Have you tried registering for Earth Explorer? I managed it without any problem, and I'm not "affiliated" to any particular "organisation". It looks like you can now get the JPGs OK at least?

Jim,

Thanks.  I have registered and hopefully tomorrow the USGS will grant me access to download more than just the JPGs.

Best,
ASLR
Title: Re: PIG has calved
Post by: Espen on November 10, 2014, 03:40:30 AM
Thanks Hunter, always at the right spot ;)
Title: Re: PIG has calved
Post by: AbruptSLR on November 10, 2014, 05:44:45 AM
NASA's IceBridge page has the following extracted statement:  "On the morning of Nov. 3, IceBridge mission planners visited the airport weather office and came back with good news. Conditions over the Pine Island and Thwaites glaciers in West Antarctica are frequently cloudy. So when the forecast showed clear conditions over the lower portion of Thwaites Glacier, IceBridge seized the opportunity to complete one of their highest priority missions.

After a few hours of flight to get to the region from southern Chile, the DC-8 descended to the day’s science target, passing over Pine Island Bay along the way. This flight measured tracks previously flown in 2011 and 2012 and lines from a joint NASA – Chilean survey in 2002."

So hopefully, we will see pictures of PIG and Thwaites from the Nov 3, 2014 flight.

Edit: The attached image shows the flight plan for that mission
Title: Re: PIG has calved
Post by: Hunter on November 10, 2014, 02:11:25 PM
Not much to see, pretty white and flat.  Here were some of the highlights

1 calving front of PIG
2 Thwaites crevasses
3 Mt murphy
4 Mt Takehe on the edge of Thwaites Glacier

 
Title: Re: PIG has calved
Post by: AbruptSLR on November 11, 2014, 08:24:15 PM
While I have discussed elsewhere in this folder that positive Nino 3.4 (MEI) values promote the advection of warm CDW into the cavity beneath the Pine Island Ice Shelf, PIIS, as we appear to be moving to an El Nino in 2015, I thought that it would be helpful to attached two images from the following reference in this thread, as such warm advection as shown in panels A and C from 2009 shown in the first attached image (the second attached image shows the correlation with the Nino 3.4 area).  Needless, to say and increase of warm CDW advection beneath the PIIS should promote calving in 2015, should the forecast El Nino event actually occur in 2015:

Pierre Dutrieux, Jan De Rydt, Adrian Jenkins, Paul R. Holland, Ho Kyung Ha, Sang Hoon Lee, Eric J. Steig, Qinghua Ding, E. Povl Abrahamsen, and Michael Schröder, 2014, "Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability", Science; Published online 2 January 2014 DOI:10.1126/science.1244341

http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract (http://www.sciencemag.org/content/early/2014/01/02/science.1244341.abstract)

http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf (http://www.sciencemag.org/content/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.pdf)

http://www.ccpo.odu.edu/~klinck/Reprints/PDF/dutrieuxScience14.pdf (http://www.ccpo.odu.edu/~klinck/Reprints/PDF/dutrieuxScience14.pdf)

Abstract:
"Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate."
Title: Re: PIG has calved
Post by: AbruptSLR on November 12, 2014, 05:18:15 PM
The two attached images are from the same Aqua photo of the PIIS on Nov 12 2014, with the second attached image with an arrow pointing to the flexural crack that Wipneus identified.  The reason that I highlight the crack in this blurry Aqua image it that as prior Aqua images do not show the crack, these images indicate that the width of the crack has likely increased sufficiently to pass the threshold resolution offered by the Aqua satellite camera.
Title: Re: PIG has calved
Post by: AbruptSLR on November 12, 2014, 05:24:51 PM
When I looked back at some earlier photos of the PIIS, I found that while I could not see the crack in the Terra images, the attached Aqua image from Oct 28 2014 clearly does show the flexural crack (indicated by the arrow).
Title: Re: PIG has calved
Post by: AbruptSLR on November 12, 2014, 10:31:23 PM
Due to cloud cover I have not posted an image of Thwaites since Oct 12 (see Reply #197); however, comparison of that Oct 12th image with the attached Terra image for Nov 12th, shows that a relative small hole has melted in the sea ice near the northwestern tip of the Thwaites Eastern Ice Shelf.  To me this relative small hole in the sea ice demonstrates that advection is actively circulating warm CDW beneath the ice shelf.
Title: Re: PIG has calved
Post by: AbruptSLR on November 17, 2014, 07:25:53 PM
As I am not set-up to manipulate the large GeoTIFF files, I limit this post of the Landsat 8 image from Nov 14 2014 to the Natural Light image. 

The first attached image of the PIIS SW Corner show increasing fractures and increasing likelihood of local calving events.

The second attached image of the general Thwaites Eastern Ice Shelf/Iceberg area confirms the Terra Nov 12 2014 image indicating that advection of warm CDW is locally melting the sea ice near the end of the Thwaites Eastern Ice Shelf even before break-up of the sea ice in this area.
Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2014, 08:06:46 PM
The attached Terra image of PIIS was taken on Nov 19 2014 and shows little change to the calving face in the past week or two.
Title: Re: PIG has calved
Post by: AbruptSLR on November 23, 2014, 07:02:03 PM
The attached "Natural Light" Landsat 8 image from Nov 23 2014 indicates that both the shear and flexural cracks in the PIIS are widening and lengthening.
Title: Re: PIG has calved
Post by: AbruptSLR on November 26, 2014, 09:58:26 PM
I will be on vacation until Dec 8 2014, so I will not be posting in that period.

Best,
ASLR
Title: Re: PIG has calved
Post by: Neven on November 26, 2014, 10:23:51 PM
Have a good vacation, ASLR.  :)
Title: Re: PIG has calved
Post by: nukefix on November 27, 2014, 01:21:28 PM
same crack seen with S-1 on 26.11.2014
Title: Re: PIG has calved
Post by: solartim27 on December 02, 2014, 11:17:24 PM
Nice article on EarthSky about B31.
http://earthsky.org/earth/nasa-is-tracking-a-gargantuan-iceberg-escaped-from-antarctica (http://earthsky.org/earth/nasa-is-tracking-a-gargantuan-iceberg-escaped-from-antarctica)
Title: Re: PIG has calved
Post by: Jim Hunt on December 03, 2014, 11:36:07 AM
Nice article on EarthSky about B31.

Given that helpful hint, B31 is plain for all to see on Worldview:

http://1.usa.gov/1yNhGRc (http://1.usa.gov/1yNhGRc)
Title: Re: PIG has calved
Post by: Wipneus on December 05, 2014, 09:30:39 AM
Nice clear weather over the PIG area and a Landsat satellite flying over. In this medium resolution (60m/pix) the crack can be clearly seen.

(click to see the 1MB image)
Title: Re: PIG has calved
Post by: Wipneus on December 05, 2014, 09:47:34 AM
Here is a hi-res detail of the crack. I cannot say that is has widened very much (still about 90 meter), but this image shows more clearly than before that is runs more or less straight through and beyond the band with ridges.
Title: Re: PIG has calved
Post by: werther on December 05, 2014, 10:39:56 AM
Thanks guys, for the great spotting!
I was surprised how fast the flow had compensated for the loss of front-stretch last year. The new crack might be an indication the process of calving is gradually getting upstream.
Title: Re: PIG has calved
Post by: AbruptSLR on December 08, 2014, 05:17:09 PM
While it is hard to say for certain, because of the cloud cover, I believe that the attached Aqua image taken Dec 7 2014 shows a relatively small calving event (if I am correct then this would account for the white flow in the notch rather than cloud cover) of the highly fractured ice at the northeast tip of the "notch".  Thus when the clouds clear, we will likely see that the notch is a little bit longer now than before yesterday.
Title: Re: PIG has calved
Post by: AbruptSLR on December 08, 2014, 05:57:10 PM
Here is a hi-res detail of the crack. I cannot say that is has widened very much (still about 90 meter), but this image shows more clearly than before that is runs more or less straight through and beyond the band with ridges.

I agree that the "flexural" crack is not widening, nor lengthening, quickly (relative to the speed of the ice flow in the PIIS).  Thus my current concern is that by about next November (2015) the ice shelf will have flowed downstream sufficiently that a new compressive strut would form (see attached image, and Replies #221 and #225) from the compression introduced from the inflow of the SW Tributary glacier, so that by Nov-Dec 2015 (or later) a new crack might form roughly parallel to the current crack, and that when the new crack ruptures it may kick-out (see panel b of the image) sufficiently to cause the current "flexural" crack to extend (abruptly) sufficiently to connect with both the "shear" cracks at the northeastern tip of the notch and at the southwestern corner.  If so, then a major calving event could occur with the new iceberg (B-32?) moving seaward at the southwestern corner and rotating about the submerged pinnacle (near the mouth of the notch), and if such a calving event were to be energetic enough, B-32?  could become unpinned and float away. 
If B-32? were to float away, it could provide enough room for a tidal (vertical bending) induced second calving event (B-33?) possibly before the end of the Austral Summer of 2015-2016, with B-33? splitting away along the postulated second "flexural" crack.  If this second calving event were to occur, it would partially (possibly by 50%) reduce the buttressing action of the PIIS against the SW Tributary glacier (which would then accelerate; which would eventually influence the shear strain along the northeastern shear margin of the Thwaites ice stream). 

It is conceivable, that this second type of calving could happen repeatedly in coming years(possibly producing future B-34, 35, etc icebergs every say 2-years).  If so this would keep the buttressing action on the SW Tributary glacier low for many years; which might then contribute to an acceleration of the Thwaites ice stream velocities (particularly if the Thwaites Eastern Ice Shelf continues to degrading in coming years due to the continued advection of warm CDW in this area).
Title: Re: PIG has calved
Post by: AbruptSLR on December 09, 2014, 08:42:36 PM
While still a little bit cloudy the attached Terra image of the PIIS for Dec 9 2014, makes it clear that indeed the notch has extended some distance to the east (likely due to a calving event on Dec 7th).
Title: Re: PIG has calved
Post by: Jim Hunt on December 10, 2014, 07:18:37 PM
While still a little bit cloudy the attached Terra image of the PIIS for Dec 9 2014, makes it clear that indeed the notch has extended some distance to the east (likely due to a calving event on Dec 7th).

Confirmed by a little bit cloudy Landsat:
Title: Re: PIG has calved
Post by: AbruptSLR on December 10, 2014, 08:10:32 PM
Jim,

Thanks for the catch on Landsat 8 for Dec 9 2014.  Based on the two attached extracts from that Landsat 8 image, I don't think that many people would be very surprised if: (a) the notch extends all the way to the end of the shear fractured ice zone (shown in the first attached image) by the end of the austral summer and thus widens and elongates the shear crack shown near the end of this shear fractured ice zone; and (b) there is more calving in the Southwest corner of the PIIS (see the second attached image); which could similarly result in the local Southwest shear cracks from extending towards what I am calling the flexural crack by the end of this austral summer.
Title: Re: PIG has calved
Post by: AbruptSLR on December 10, 2014, 09:08:03 PM
I thought that I would post this Nov 14 2014 Landsat 8 image of the residual Thwaites Ice Tongue and Eastern Ice Shelf to illustrate that once the pinned remains of the old Thwaites Ice Tongue gets unpinned and floats away as an iceberg, then all of the upstream ice is in the form of bergy bits that will not become pinned and will just float away, which will essentially relieve any remaining buttressing action on the Thwaites ice stream that fed the old Thwaites Ice Tongue.
Title: Re: PIG has calved
Post by: AbruptSLR on December 11, 2014, 05:28:39 PM
The attached Terra image from Dec 11 2014, appears to indicate a very small minor possible calving event near the tip of the notch.
Title: Re: PIG has calved
Post by: AbruptSLR on December 13, 2014, 01:36:09 AM
I thought that it might be interesting to see in the attached Aqua image of Thwaites for Dec 12 2014, that there is still a fairly significant amount of sea ice around the Thwaites Ice Shelf & Residual Ice Tongue, possibly because the air temperatures in this area have been colder than normal for this time of year:
Title: Re: PIG has calved
Post by: AbruptSLR on December 16, 2014, 12:40:37 AM
The two attached images extracted from the Landsat 8 image for Dec 14, 2014, shows that both the notch and the Southwest corner areas of the Pine Island Ice Shelf, PIIS, are continuing to slowly degrade.
Title: Re: PIG has calved
Post by: AbruptSLR on December 18, 2014, 08:27:01 PM
The first attached Landsat8 image of the area near the tip of the Thwaites Eastern Ice Shelf taken Dec 14 2014 shows the continued impact of advection (which is less for Thwaites than for PIG) forming a small polynya between the tip of the Thwaites Eastern Ice Shelf and the grounded iceberg at the end of the residual Thwaites Ice Tongue.

The second attached Terra image of the PIIS for Dec 18 2014 indicates that a very minor amount of calving occurred of the fractured glacial ice at the tip of the notch on Dec 17 2014.
Title: Re: PIG has calved
Post by: AbruptSLR on December 19, 2014, 07:08:19 PM
The first attached Landsat 8 image of the PIIS notch tip on Dec 18 2014 shows that indeed there was a minor calving event at the tip of the notch on Dec 17 2014.  Also, this first image shows that location of the shear cracks at the notch tip in regards to the location of the "Flexural Crack", indicating the feasibility of the idea that a new "Flexural Crack" parallel to the current "Flexural Crack, possibly forming as early a Nov 2015 (with the timing linked to the ice velocity of the PIIS ice stream), by inducing a "kick" that would extend the existing cracks to form a major calving mechanism.

The second image show a Terra image of the PIIS for Dec 19 2014; which I provide as a reference, for comparison with possible future minor calving events this austral summer.
Title: Re: PIG has calved
Post by: AbruptSLR on December 28, 2014, 01:22:16 AM
Comparing the attached Aqua image of the PIIS from Dec 27 2014, with the Terra image for Dec 19 2014 in my preceding post, it is clear that a meaningful (but small) calving event in the week in between these two dates in the Southwest Corner of the PIIS (also the "flexural" crack is very clear in this Aqua image):
Title: Re: PIG has calved
Post by: AbruptSLR on December 29, 2014, 09:39:48 PM
Per the first two attached Aqua images of the PIIS (one natural light and the other filtered to differentiate ice and clouds, respectively) from Dec 29 2014, it looks like the Southwest corner of PIIS is being reconfigured (possibly due to compression) with some associated calving debris in the adjoining ocean.  Based on the third attached Aqua image of the PIIS taken yesterday, it appears that this reconfiguration began on Dec 28 2014 and is continuing into today.
Title: Re: PIG has calved
Post by: AbruptSLR on January 03, 2015, 01:05:16 AM
While not 100% certain, the attached Terra image of the PIIS for Jan 2 2015 indicates that meaningfully calving event has occurred in the SW corner:
Title: Re: PIG has calved
Post by: AbruptSLR on January 07, 2015, 09:54:31 PM
The two attached images are from the Landsat8 picture taken on January 6 2015 and the first image shows the Southwest Corner has a free-floating iceberg that has not yet been displaced from the calving face, while the second attached image shows that the notch and the "flexural" crack are slowly degrading (possibly on pace to facilitate a major calving event in the Nov to Dec 2015 timeframe).
Title: Re: PIG has calved
Post by: AbruptSLR on January 13, 2015, 10:16:36 PM
The attached Terra image of PIIS taken on Jan 13 2015 shows that the iceberg that had been moving around within the small Southwest notch has finally floated away from the calving face.
Title: Re: PIG has calved
Post by: Wipneus on January 15, 2015, 06:49:58 AM
Sequence of two Sentinel-1A panorama quick-look images separated by 3 months in time.
Title: Re: PIG has calved
Post by: AbruptSLR on January 15, 2015, 05:55:51 PM
Wipneus,

Thanks for the great Sentinel-1A sequence that not only shows how quickly the PIIS is extending its calving face seaward, but also indicates to me that the residual Thwaites Ice Tongue is also moving seaward and may only be held in-place by the surrounding land-fast sea ice.  While I do not expect the PIIS to have another major calving event until the Nov-Dec 2015 timeframe, it would be interesting if the residual Thwaites Ice Tongue were to float away once the sea ice breaks-up later this austral summer.

Also, the attached PIIS Landsat 8 image is from Jan 15 2015.
Title: Re: PIG has calved
Post by: Yuha on January 16, 2015, 12:16:40 AM
There's also a possibility of a medium size calving event at the eastern end of Thwaites calving front.
That would be an ice berg of about the size of Manhattan if it calves off in one piece.


Title: Re: PIG has calved
Post by: AbruptSLR on January 19, 2015, 08:20:28 PM
There's also a possibility of a medium size calving event at the eastern end of Thwaites calving front.
That would be an ice berg of about the size of Manhattan if it calves off in one piece.

As the attached Aqua image of the Thwaites Ice Shelf for Jan 19 2015 indicates, the break-up of some of the previous fast sea ice on the eastern edge of the Thwaites Ice Shelf is allowing for the Manhattan sized iceberg for the calving event that Yuha discusses, to move away from the calving face.
Title: Re: PIG has calved
Post by: AbruptSLR on January 26, 2015, 06:24:39 PM
While the attached Aqua image of the PIIS from Jan 26 2015 is not much different than the Jan 13th image shown in Reply #275, I thought that I would post it and note that even if the extent of the notch is not growing rapidly nevertheless:

(a) As the ice flow velocity increases the resistance of the shear margins are decreasing (see the link regarding MacGregor et al 2012)

http://www.skepticalscience.com/West-Antarctic-Ice-Shelves_U-of-Texas-at-Austin.html (http://www.skepticalscience.com/West-Antarctic-Ice-Shelves_U-of-Texas-at-Austin.html)

(b) Due to both basal ice melting and ice flow acceleration the thickness of the PIIS is decreasing and thus its propensity to calve is increasing and its buttressing action is decreasing.
Title: Re: PIG has calved
Post by: AbruptSLR on February 05, 2015, 10:18:21 PM
The attached Terra image of Thwaites was taken today (Feb 5 2015), and indicates that the land-fast ice in this area is starting to break-up which will likely release a number of bergy bits that have been calved from both the Eastern Thwaites Ice Shelf and the residual Thwaites Ice Tongue in the past year, or so.
Title: Re: PIG has calved
Post by: AbruptSLR on February 06, 2015, 08:31:20 PM
The first attached image of the ASE taken Feb 6 2015 shows that the sea ice in this area is slowly starting to break-up and retreat from the embayment.  It will interesting to watch this sea ice in the coming weeks.
Title: Re: PIG has calved
Post by: Wipneus on February 09, 2015, 02:48:05 PM
Here is a sequence composed of Landsat images (30m/pix) from Dec 4 and Feb 6, spanning a 64 day interval.
Measuring pixel movement, using the 15m native resolution, the ice moved about 701.5 meter. That translates to an average speed of 11 m/day, the highest figure that I measured yet.

The "crack" has widened a little, but the visible part is also much longer. Especially to the west (right in this image).

A next crack-like feature, parallel to this one, is faintly visible upstream. Whether this is an optical aberration or really a new crack is as yet an open question.

(click to see the 2.8 MB animation)

Title: Re: PIG has calved
Post by: Jim Hunt on February 09, 2015, 04:28:57 PM
Thanks Wipneus. Is there any chance you could try something similar for the Roi Baudouin Ice Shelf. Here's the reason I ask:

http://GreatWhiteCon.info/2015/02/new-antarctic-sea-ice-resources/ (http://GreatWhiteCon.info/2015/02/new-antarctic-sea-ice-resources/)

While large icebergs calve regularly from fast-flowing ice shelves in West Antarctica, the coast of cooler, drier East Antarctica tends to be less active. That made it a mild surprise when a 70-square-kilometer chunk of ice broke off from the King Baudouin Ice Shelf in January 2015. The last time that part of King Baudouin calved such a large iceberg was in the 1960s.

I hope all the associated information is OK with you?
Title: Re: PIG has calved
Post by: AbruptSLR on February 22, 2015, 05:27:25 PM
The two attached Terra images of the PIIS for Feb 22 2015 (one with natural light and one with a red filter, respectively) clearly indicate a localized calving event within the "notch".  I believe that such localized calving events are dominated by the influence of the advection of warm CDW beneath both the local sea ice and beneath the PIIS itself.  Furthermore, there are forecasts of a moderately strong classical El Nino event by the boreal Fall (austral Spring) of 2015; which could intensify the flow of such warm CDW beneath the PIIS by November 2015; which in turn might promote a possible major calving event by Nov - Dec 2015.

Also, I note that such localized calving events in the "notch" reduces the boundary restraints that are currently slowing the elongation of the "flexural" crack in the PIIS (documented by Wipneus).
Title: Re: PIG has calved
Post by: nukefix on February 23, 2015, 05:32:52 PM
I do not see anything unusual:

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20150221T091035_74F7_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20150221T091035_74F7_S_1.final.jpg)
Title: Re: PIG has calved
Post by: AbruptSLR on February 23, 2015, 08:08:51 PM
I do not see anything unusual:


When comparing to the Landsat8 image from Feb 6 2015 in Reply #283, it is clear to me that the notch is longer than in the attached first Polarview image from Feb 21 2015.  Thus either Terra image from Feb 22 2015 is showing snow blown into the seawater in the notch, or there was an actual calving event of the shear fractured glacial ice at the tip of the notch on or near that data.

The second attached image is a Terra photo of PIIS on Feb 23 2015.

The third attached image is an Aqua photo of Thwaites on Feb 23 2015.

The fourth attached image of the ASE is also from Feb 23 2015 and shows that the sea ice in the embayment may slowly be breaking-up.
Title: Re: PIG has calved
Post by: Sleepy on February 23, 2015, 08:32:54 PM
Note that the polarview image is from 20150221. The brake up ASLR noticed was on the 22:nd.
A small animation from terra Feb 21-23.
Title: Re: PIG has calved
Post by: solartim27 on February 24, 2015, 06:02:40 PM
Looks like some wind kicked up around the corner of Thwaites.  I'm having trouble wrapping my head around the change here.  Definately some sea ice moving, but was there a calving or further breakup of landfast ice? 
Both images have a date stamp of 2/24.
Title: Re: PIG has calved
Post by: AbruptSLR on February 24, 2015, 06:11:41 PM
Looks like some wind kicked up around the corner of Thwaites.  I'm having trouble wrapping my head around the change here.  Definately some sea ice moving, but was there a calving or further breakup of landfast ice? 
Both images have a date stamp of 2/24.

solartim,

Thanks for the nice images (attached also is a closer view of the Terra image on Thwaites from today).  As discussed earlier in this thread a meaningful chunk of glacial ice calved from the Southeastern portion of the Thwaites Eastern Ice Shelf a few months ago, but was trapped by the fast sea ice.  So now that the sea ice is slowly breaking-up this calved iceberg is now slowly floating away.

Best,
ASLR
Title: Re: PIG has calved
Post by: Sleepy on February 25, 2015, 01:14:29 PM
Polarview from today. How long before that entire section leaves the port?
Title: Re: PIG has calved
Post by: icefest on February 25, 2015, 01:29:41 PM
That crack is getting closer and closer.....
Title: Re: PIG has calved
Post by: AbruptSLR on March 07, 2015, 01:24:51 AM
The attached Landsat8 image of the Thwaites gateway on March 6 2015 shows that the sea ice to the North and East is moving away, but that there is still a significant amount of fast sea ice to the West of the Thwaites Eastern Ice Shelf.
Title: Re: PIG has calved
Post by: Sleepy on March 07, 2015, 07:29:47 AM
The crack is more visible on Polarview from 20150305.
Title: Re: PIG has calved
Post by: AbruptSLR on March 07, 2015, 06:11:25 PM
I provide the four attached images of the PIG area in order to document an apparent calving event of grounded glacial ice (not floating) in the area immediately to the Southwest of the PIIS (so I have labeled the images PIG Southwest Corner to differentiate from my other PIIS images).

The first Terra image from March 6 2015 shows this area before the calving event.  The second Landsat8 image from March 6 2015 shows this area immediately after the primary calving event.  The third Aqua image from March 6 2015 shows some secondary calving following the primary calving activity.  Finally, the fourth attached image from this morning, March 7 2015 shows the about the same size debris field floating in the ocean at the calving site as the Aqua image from the evening of March 6.

While I do not know why this ice calved (it may be normal calving activity); however, it could be related to warm CDW water advecting near the calving event grounding line, and/or could be related to a compressive stress field on this PIG Southwest Corner area as the PIIS accelerates and bears harder against this grounded corner glacial ice.
Title: Re: PIG has calved
Post by: Wipneus on March 11, 2015, 11:51:38 AM
Close-up of the crack seen by Landsat 8 this time. The crack is 105-120m wide over a long range and appears slowly widening. The length of the crack is increasing also, I have put some arrows at the end points where I can reliably identify the crack.
The second upstream crack is now visible without a doubt. Marked with an arrow as well.

(click to see the full resolution image)
Title: Re: PIG has calved
Post by: Jester Fish on March 11, 2015, 06:42:45 PM
Thanks Wipneus. Could you add this frame to your animation from Feb 9?  I'm trying to get a sense of the rate of expansion- both width and length - of the crack.
Title: Re: PIG has calved
Post by: nukefix on March 11, 2015, 06:52:50 PM
It's just a matter of time...tidal flexing etc. will propagate the crack through sooner or later. When was the last time PIG had a major calving event? A few years at least?
Title: Re: PIG has calved
Post by: AbruptSLR on March 11, 2015, 07:06:57 PM
It's just a matter of time...tidal flexing etc. will propagate the crack through sooner or later. When was the last time PIG had a major calving event? A few years at least?

If my speculation in Reply #261 is correct, then this up-coming calving event may be different than the July 2012 to November 2012 calving event (see Replies 225 and 230), in that the failure plane may extend from the "flexural" crack towards the shear cracks in the Southwest corner (see attached Landsat8 image from March 8 2015), and then rotate outwards around the submerged pinnacles to float away.  If so this different calving mechanism is important because it would result in a new calving face that is further upstream than the 2012 calving event (see Reply 230); which would relieve some of the buttressing on the Southwest Tributary Glacier, which would help to destabilize the Thwaites Gateway.

Edit: As a reminder I have stuck my neck-out and projected that a new major calving event could occur in the Nov-Dec 2015 timeframe (based on geometry and the rate of ice flow velocity for the PIIS).  This would be followed by successive major calving events every two to three years with each new calving face moving further upstream (thus successively relieving buttressing from the Southwest Tributary Glacier).
Title: Re: PIG has calved
Post by: Wipneus on March 11, 2015, 07:12:42 PM
Thanks Wipneus. Could you add this frame to your animation from Feb 9?  I'm trying to get a sense of the rate of expansion- both width and length - of the crack.

The satellite is here in a different orbital position than in the two frames in that animation, with very different sun position. That influences the appearance of the crack, including width and length.
Unfortunately the image from Mar 10 when the Landsat was in the correct position was cloudy.

I plan to do some more analysis on the Sentinel images at some day though. I think a nice long sequence of those should be possible.
 
Title: Re: PIG has calved
Post by: AbruptSLR on March 19, 2015, 10:25:49 PM
I post this Terra image of Thwaites for March 19 2015, because I think that it is interesting that while there is some thin newly frozen sea ice, some of the older thicker fast sea ice has recently broken free from the east side of the Thwaites Eastern Ice Shelf.
Title: Re: PIG has calved
Post by: AbruptSLR on March 23, 2015, 06:02:04 PM
The attached image is from the Landsat8 satellite for March 17 2015.  To me this image indicates some of the impacts of the relatively high (recently accelerated) ice flow velocity of the PIIS, including: (a) shear cracks in the northern edge of the Southwest Tributary Glacier at its confluence with the PIIS; (b) a crevasse formation in the grounded glacial ice in the southwest corner between the PIIS and the Southwest Tributary Glacier; (c) widening of the "flexural" crack in the PIIS; (d) compressive folding of the floating glacial ice at the southwest corner of the PIIS; and (e) widening of the shear cracks at the southwest corner of the PIIS.

All of these indications encourage me to think that there may well be a major calving of the PIIS in the Nov to Dec 2015 timeframe.
Title: Re: PIG has calved
Post by: GeoffBeacon on March 25, 2015, 10:33:23 PM
Just seen a report from the European Space Agency. Is this news?

This image combining two scans by Sentinel-1A’s radar shows that parts of the Pine Island glacier flowed about 100 m (in pink) between 3 March and 15 March 2015. Light blue represents stable ice on either side of the stream.

http://www.esa.int/spaceinimages/Images/2015/03/Pine_Island_Glacier_on_Sentinel-1A_s_radar (http://www.esa.int/spaceinimages/Images/2015/03/Pine_Island_Glacier_on_Sentinel-1A_s_radar)
Title: Re: PIG has calved
Post by: AbruptSLR on March 25, 2015, 11:47:11 PM
Geoff,

Thanks as this information was news to me; however, further up this thread Wipneus makes the following statement (which indicates comparable ice flow velocities)

"Here is a sequence composed of Landsat images (30m/pix) from Dec 4 and Feb 6, spanning a 64 day interval.
Measuring pixel movement, using the 15m native resolution, the ice moved about 701.5 meter. That translates to an average speed of 11 m/day, the highest figure that I measured yet."

Best
ASLR
Title: Re: PIG has calved
Post by: crandles on March 26, 2015, 01:06:55 AM
one of the fastest ice streams on the continent, with an average of over 4 km per year

so 100m in 12 days is under 75% of average and 701.5m in 64 days is only just average or probably below average. Why is the fastest speed Wipneus measured likely to be below average? Is that odd or is there reason why it is difficult to measure when it is moving at above average speed?
Title: Re: PIG has calved
Post by: Gray-Wolf on March 26, 2015, 10:32:21 AM
Didn't we find that surface winds over Nina periods slowed the warm water impacting the glacier front and so its flow rates? Now we have been nino or near nino for a while maybe we ought to expect the 'slowdown' in mass loss that we had been seeing now reverse as the surface winds swing around and warm waters are helped toward the calving front/grounding line?
Title: Re: PIG has calved
Post by: AbruptSLR on March 26, 2015, 04:03:06 PM
one of the fastest ice streams on the continent, with an average of over 4 km per year

so 100m in 12 days is under 75% of average and 701.5m in 64 days is only just average or probably below average. Why is the fastest speed Wipneus measured likely to be below average? Is that odd or is there reason why it is difficult to measure when it is moving at above average speed?

4000m/365 = 11m/day, which equals the speed that Wipneus measured.  Furthermore, depending on how the researchers treat end dates, March 3rd to 15th might possibly be 11 days and not 12, so 100/11 = 9 m/day, which might be within the natural fluctuations of the PIIS ice flow (including ENSO, weather, & observational uncertainty).
Title: Re: PIG has calved
Post by: AbruptSLR on March 26, 2015, 10:43:37 PM
Just for fun, I post the first attached Worldview image of the Ferrigno Ice Tongue on March 8 2015; and for comparison I provide the second attached image showing that the Ferrigno Ice Tongue surged in late Summer of 2012 and then calved back to its equilibrium condition by Feb 2013, and it seems to have stayed in equilibrium since then.
Title: Re: PIG has calved
Post by: Sleepy on March 27, 2015, 08:10:44 AM
From crandles post here, http://forum.arctic-sea-ice.net/index.php/topic,622.msg48780.html#msg48780 (http://forum.arctic-sea-ice.net/index.php/topic,622.msg48780.html#msg48780)

And a quote from Sciencemag http://news.sciencemag.org/climate/2015/03/antarctica-rapidly-losing-its-edge (http://news.sciencemag.org/climate/2015/03/antarctica-rapidly-losing-its-edge)
Even so, the overall picture they report online today in Science is grim: The 18-year record suggests that the average loss in volume of Antarctica’s ice shelves across the entire continent has accelerated significantly in the last decade. From 1994 to 2003, the overall loss of ice shelf volume across the continent was negligible: about 25 cubic kilometers per year (plus or minus 64). But from 2003 to 2012, that number jumped to 310 cubic kilometers per year (plus or minus 74). That rapid acceleration was particularly apparent in the WAIS, where volume losses increased by 70% in the last decade. In the hot spots of the Amundsen and Bellinghausen seas, the ice shelves lost 18% of their thickness in less than 10 years.

The graph below is from the supplement that's free http://www.sciencemag.org/content/suppl/2015/03/25/science.aaa0940.DC1/Paolo-SM.pdf (http://www.sciencemag.org/content/suppl/2015/03/25/science.aaa0940.DC1/Paolo-SM.pdf)
Title: Re: PIG has calved
Post by: AbruptSLR on March 27, 2015, 06:21:53 PM
The attached Worldview image of the PIIS for March 27 2015 shows that the "notch" has extended slightly as compared to the March 17 2015 Landsat 8 image shown in Reply #302.
Title: Re: PIG has calved
Post by: Wipneus on March 29, 2015, 03:01:39 PM
Detail of the "crack" with the Landsat 8 camera "moving" with the upstream part of the glacier.
The downstream part can be seen to be separating, visually even more clearly than judging the width of the crack.
The total relative displacement between October 8 and March 17 is 2x3 (down x left) 15m pixels, about 50 meters. 
Title: Re: PIG has calved
Post by: Yuha on March 29, 2015, 04:01:57 PM
The downstream part can be seen to be separating, visually even more clearly than judging the width of the crack.
The total relative displacement between October 8 and March 17 is 2x3 (down x left) 15m pixels, about 50 meters. 

It seems the downstream part is not moving straight downstream but quite a bit sideways too.
Title: Re: PIG has calved
Post by: Shared Humanity on March 29, 2015, 04:43:41 PM
With a continuous crack that grows this quickly, is it possible that the lead portion of  PIIS has already completely separated from the ice  behind it?
Title: Re: PIG has calved
Post by: AbruptSLR on March 29, 2015, 05:58:26 PM
The downstream part can be seen to be separating, visually even more clearly than judging the width of the crack.
The total relative displacement between October 8 and March 17 is 2x3 (down x left) 15m pixels, about 50 meters. 

It seems the downstream part is not moving straight downstream but quite a bit sideways too.

Yuha,

You make a good observation; which could (possibly) be taken as evidence supporting my hypothesis that the next major calving event for the PIIS will first swing seaward from the Southwestern end of the calving face, thus pivoting about the pinnacle at the opposite end of the calving face.  If true this would represent a change in previous calving behavior and would support my "compressive field" interpretation (with the compression coming from the Southwest Tributary Glacier running into the PIIS) that I started outlining in Reply #225.

SH,

If my "compressive field" interpretation is correct then there is very little chance that the portion of the PIIS seaward of the (flexural) crack has completely separated from the upstream portion of the PIIS as at least the Southwest corner should still be in compression and the pinnacle is probably still restraining the Northeast end of the (flexural) crack.  Furthermore, 50-m of crack widening can easily be accounted for by stain deformations without any need for invoking rigid body translations/rotations.

Best,
ASLR
Title: Re: PIG has calved
Post by: AbruptSLR on April 08, 2015, 12:16:00 AM
I am posting this April 7 2015 Terra image of Thwaites as it may well be the last of this season (due to cloud cover & loss of daylight), and it shows that while sea ice is current extending around Antarctica, locally it is still breaking-up north of Thwaites.
Title: Re: PIG has calved
Post by: Wipneus on April 09, 2015, 11:00:17 AM
The crack in hi-res Sentinel images. The images are from 2014-10-10 and 2015-04-08, separated by 180 days or 12 Sentinel cycles. The glacier moved in the middle about 1980.4 m, 11.0 m/day.
The images are aligned on the crack which is seen lengthening, widening and - if I read the shadows in this SAR image correct - deepening.

click to open a 3.5 MB animation.
Title: Re: PIG has calved
Post by: solartim27 on April 21, 2015, 07:32:22 PM
Looks like some cracks are forming at the top of the notch heading towards the larger middle crack? (From Polar View 4/19, 32MB pic http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20150419T035507_7940_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20150419T035507_7940_S_1.final.jpg) )

Edit:  circled the area I was looking at
Title: Re: PIG has calved
Post by: nukefix on May 06, 2015, 05:51:38 PM
Here's an RGB-composite of two S-1 acquisitions:

R = B = 19.4.2015
G = 1.5.2015

Movement of the crack in these 12 days appears to be approximately 200m ~= 17m/day ~= 6km/year.
Title: Re: PIG has calved
Post by: AbruptSLR on May 06, 2015, 06:36:56 PM
nukefix,

Thanks for the great image & calcs.  If correct, your 17m/day represents a significant acceleration of the PIIS ice flow velocity from the 11m/day value that Wipneus calcs in earlier posts.

As we are currently in an El Nino condition and as the ABSL has been positioned for the past couple of months to direct/blow warm CDW directly in to the ASE (see the attached Earth 850 hPa Wind & MSLP Map for May 6 2015); which in past has been proven to accelerate PIIS ice velocities by advecting greater volumes of warm CDW directly beneath the ice shelf.

If so, then my forecast of a major PIIS calving event in the Nov to Dec 2015 timeframe still seems on track.

Best,
ASLR
Title: Re: PIG has calved
Post by: oren on May 06, 2015, 10:25:55 PM
Here's an RGB-composite of two S-1 acquisitions:

R = B = 19.2.2015
G = 1.5.2015

Movement of the crack in these 12 days appears to be approximately 200m ~= 17m/day ~= 6km/year.

I guess the baseline is 19.4.2015 ?
Title: Re: PIG has calved
Post by: nukefix on May 06, 2015, 10:29:47 PM
ASRL, please note that my estimate has a much larger margin of error as I eyeballed the movement during 12 days, while Wipneus had 12*12=144 days so a much better signal to estimation error ratio. It would be interesting to check whether actual acceleration has taken place.
Title: Re: PIG has calved
Post by: nukefix on May 06, 2015, 10:31:00 PM
I guess the baseline is 19.4.2015 ?
Yes, thanks, fixed.
Title: Re: PIG has calved
Post by: AbruptSLR on May 06, 2015, 10:59:51 PM
ASRL, please note that my estimate has a much larger margin of error as I eyeballed the movement during 12 days, while Wipneus had 12*12=144 days so a much better signal to estimation error ratio. It would be interesting to check whether actual acceleration has taken place.

Thanks for the clarification.  It would be great if you could provide periodic updates through the dark austral winter.
Title: Re: PIG has calved
Post by: Wipneus on May 07, 2015, 07:08:54 AM
Let me explain how I arrive at my estimated velocity from two images acquired from identical orbital positions:

- load the two images as layers in The Gimp;
- Clicking the visibly of the top layer you can detect whether parts of the images are out of alignment. Shift the images until the rocks in the images are perfectly aligned: remaining movements  are due to genuine ice movements;
- to measure the movement of some feature, e.g. "the crack", move the top layer again until the object is aligned to perfection. Note the number of pixels that the top image was shifted and calculate speed.

With images from 2015-04-20 and 2015-05-02 I measure a shift of 14x1pixels. At 10 m/pix and 12 days this translates to about 11.7 m/day.
The uncertainty in the procedure is at best 2 pixels (one pixel in both steps 2 and 3), but honestly could be two times that amount.
So my result would be reported as 12 +/-4 [m/day].

Of course letting the computer doing the alignment capable would reduce the uncertainty to sub-pixel values. To reliably detect acceleration it seems required.
Title: Re: PIG has calved
Post by: nukefix on May 07, 2015, 12:26:55 PM
Wipneus your estimate is better, it looks like I had a shift in the co-registration of images. I processed the data again and now I'm getting values close to 140m in 12 days.

The S-1 orbits are good enough that sub-pixel co-registration should be possible with orbit data alone. I'm trying to figure out how best to do it in the S-1 toolbox. It's quite easy to script the operations so that it would be possible to add new images to the stack semi-automatically each time a new image arrives.

Title: Re: PIG has calved
Post by: solartim27 on May 09, 2015, 09:38:04 AM
Elvis hasn't left the building, but his bag is packed and he's heading for the elevator.
Title: Re: PIG has calved
Post by: AbruptSLR on May 10, 2015, 01:39:10 AM
For what it is worth, per the attached Earth Surface Wind & Temperature Map for May 9 2015 for Antarctica; the surface air temperature at the PIG is about 1.8C.
Title: Re: PIG has calved
Post by: AbruptSLR on May 10, 2015, 03:43:52 PM
Not to be the master of the obvious, but strong El Nino events telecommunicate atmospheric energy from the Tropical Pacific to the West Antarctic focused on the ASE.  Therefore, as we are currently in a mild El Nino condition and are projected to reach a strong El Nino condition as soon as July, the fact that the two attached NOAA daily temp, and temp anom, maps (respectively) for May 9 2015 show the ASE to currently be above freezing (with a temp anom of over 20 C); indicates to me that ice mass loss (& associated major/minor calving) will likely occur at an accelerated level for at least the next nine months (or for however long the current El Nino condition lasts).
Title: Re: PIG has calved
Post by: Wipneus on June 28, 2015, 03:19:04 PM
Time for an update. I choose sentinel IW (10m/pix) images from May 2 and June 19, 48days or 4 Sentinel cycles.
The "crack" has widened by about 10-20m, now about 140m in the middle. It has also got quite visibly longer, especially to the West (right in the image).
Some of the cracks in the shearing region can be seen getting longer as well.
I estimate the main glacier has moved about 55x7 (down x left) pixels. That works out to about 11.6 m/day. No winter slowdown for the PIG.

Final image rendered at 20m/pix to keep the image size reasonable. Click to start the animation.
Title: Re: PIG has calved
Post by: Buddy on June 28, 2015, 10:28:27 PM
That puppy does NOT have a lot of life left.  Within 2 years it will be toast...  Nice graphic.
Title: Re: PIG has calved
Post by: AbruptSLR on July 06, 2015, 09:59:53 PM


The linked article indicates that between March 3 and March 15 2015, the PIG ice stream flowed at a rate of 4,000 m/yr, or 11 m/day; which very closely matches Wipneus' value:

http://www.livescience.com/50254-fast-flow-pine-island-glacier.html (http://www.livescience.com/50254-fast-flow-pine-island-glacier.html)

One of West Antarctica's largest glaciers surged a staggering 325 feet (about 100 meters) in less than two weeks this month, the European Space Agency reports.
Two radar images from the ESA's Sentinel-1A satellite on March 3 and March 15 reveal parts of the enormous Pine Island Glacier and its floating ice shelf making a swift trek toward the sea. The wild race to sea is typical for Pine Island Glacier, which flows up to 13,120 feet (4,000 m) every year.

Title: Re: PIG has calved
Post by: solartim27 on July 30, 2015, 10:35:01 PM
BYE BYE
Edit:  GIFed it up, images from 7/17 to 7/30.  There was another shot at 7/23, with no sign of the collapse coming.

Edit:  Added the frame for the 23rd because you can see the ice field collapsing.
Title: Re: PIG has calved
Post by: AbruptSLR on July 30, 2015, 11:02:55 PM
BYE BYE

That looks like ice bergs have split-off near the submerged pinnacle.

That looks like the break goes all the way back to the crack that Wipneus has been documenting (leaving a chunk of the shelf left dangling on the submerged pinnacle), this is a major calving event in the middle of the austral winter and could soon relieve some buttressing support for the SW Tributary Glacier.

Also, this attached image show the condition of the Thwaites Ice Shelf/Tongue on July 30 2015, per Polarview
Title: Re: PIG has calved
Post by: Rubikscube on July 30, 2015, 11:58:01 PM
Spectacular. It looks like the SE corner got a sizable forward nudge as well, but failed to snap. I'm looking forward to a closer inspection of the central crack, and your further analysis of course.
Title: Re: PIG has calved
Post by: AbruptSLR on July 31, 2015, 12:31:29 AM
Spectacular. It looks like the SE corner got a sizable forward nudge as well, but failed to snap. I'm looking forward to a closer inspection of the central crack, and your further analysis of course.

Rubikscube,

I believe that you are referring to the NW corner that nudged forward; however, I believe that it has snapped free of the rest of the PIIS but that it is grounded on the submerged pinnacle shown in the attached image (showing the mid-January 2014 grounding line location).  I looks to me like this mode of this spectacular calving event was trigger by compressive stresses induced in the PIIS by the SW Tributary Glacier.

Best,
ASLR

PS: South is to the right of this image
Title: Re: PIG has calved
Post by: AbruptSLR on July 31, 2015, 01:21:52 AM
For those who have a hard time imagining how compression from the SW Tributary Glacier could contribute to today's calving pattern, I re-post the attached image showing how a solid subjected to external compressive loading develops internal stress patterns that kick out laterally, thus causing splitting tension parallel to the axis of compressive loading>
Title: Re: PIG has calved
Post by: sidd on July 31, 2015, 05:20:44 AM
Nice,scary,catch, tanx. PIG is approx 20-25Km across ?
Title: Re: PIG has calved
Post by: Wipneus on July 31, 2015, 09:11:06 AM
Wonderful. Here is a sequence 12 days apart, that means the Sentinel is in identical orbital position.
Resolution of the image is 120m/pixel, implying the width of the image is about 68km.

There are hi-res images available from the 24th and 25th, but I have some trouble downloading it from the data hub. The zip files keep being corrupted in different positions.
Title: Re: PIG has calved
Post by: Wipneus on July 31, 2015, 11:58:15 AM
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)
Title: Re: PIG has calved
Post by: oren on July 31, 2015, 03:40:47 PM
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)

Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

BTW that huge crack is so impressive.
Title: Re: PIG has calved
Post by: AbruptSLR on July 31, 2015, 04:17:59 PM
Nice,scary,catch, tanx. PIG is approx 20-25Km across ?

Yes, for convenience I provide the attached 2012 image with an embedded scale in km's for reference.
Title: Re: PIG has calved
Post by: Rubikscube on July 31, 2015, 04:20:39 PM
Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

BTW that huge crack is so impressive.

The rapid lengthening and widening of various cracks is itself part of the collapse process that ultimately result in the ice breaking off. I believe that is what is being referred to.

I believe that you are referring to the NW corner that nudged forward;

Yes, wrong hemisphere :)
Title: Re: PIG has calved
Post by: Yuha on July 31, 2015, 04:30:40 PM
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)

Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

Oren, look at he dates. The collapse happened some time between July 25 and July 30.
Title: Re: PIG has calved
Post by: AbruptSLR on July 31, 2015, 04:30:59 PM
Here is a sequence of three hi-res images (10m/pix, here rendered to 30m/pix for size). I slap myself on the head: this collapse has been visible for most of July.

(click to start the 3.5 MB animation)

Stupid question: where exactly is the collapse in the animation? Am I being blind, or maybe it is cut off at the bottom? I don't know much about the PIG, but I am quite confused here.

BTW that huge crack is so impressive.

If you look at the sketch in Reply #336, you will see that compression from the Southwest Tributary Glacier (at right angle to the PIIS), creates the splitting tension crack shown by Wipneus, but which also creates a lateral (downstream) kick at the middle of the ice shelf.  As the Northwest corner of the ice shelf is pinned at the bottom by a submerged pinnacle, it is natural (by fracture mechanics) that the lateral (downstream) kick would form a failure mechanism by extending the splitting tension crack down to the Southwest corner (which is not pinned).  Which this calving mechanism is formed (as shown in Wipneus's animation) it is just a matter of time, kinematics and boundary conditions for the lateral (downstream) kick to calve-off the middle wedge of an iceberg shown by solartime27 (leaving the Northwest iceberg pinned in place but rotated and the Southwest iceberg floating away faster than the middle wedge).
Title: Re: PIG has calved
Post by: A-Team on July 31, 2015, 04:36:19 PM
I slap myself on the head: this collapse has been visible for most of July.
Let's keep an eye then on the new crack, top center below. The fact remains, even if Sentinel scenes are auto-streamed into a video, somebody has got to watch that video. However it's feasible to set up an auto-alert by differencing frames, not so dissimilar to wildlife camera motion detectors.

Followed by auto-posting and subsequent Typepad notifications, maybe in the future an auto-journal submission that robotic crawling could utilize use for review articles, future sea level rise revisions and proportionate auto-increasing of carbon taxes.

Do you have earlier frames handy? To date the new crack, see when it developed, whether it is progressing. Also one longitudinal crack, bottom left, seems to pre-date the horizontal developments.

It is parallel to the main one because there is more frictional drag on the right side, meaning transverse shear leading to brittle failure. Petermann also has this half-herringbone pattern. The ice in the middle perhaps has a different character, maybe colder. The whitish areas on the sides where motion transitions from 3/12 pixels a day to 0 might be warmer, softer, smoother so more reflective of the radar beam.

In glaciology, they would go on here about the Cauchy stress tensor, deviatoric stress component, strain rates and so forth. It's all in Cuffey & Paterson or at this user-friendly Antarctic link below. There was a nice graphical display on that recently for Larsen B. http://www.antarcticglaciers.org/modern-glaciers/longitudinal-stress/ (http://www.antarcticglaciers.org/modern-glaciers/longitudinal-stress/)

Fascinating to watch how gaps in the crack get filled in. The piece about to shatter is pivoting, somewhat awkwardly, causing secondary longitudinal cracks to extend on the right side. Here is a shorter smaller faster version of W's animation for any busy ice executives who might stop by.
Title: Re: PIG has calved
Post by: Yuha on July 31, 2015, 04:50:12 PM
I looks to me like this mode of this spectacular calving event was trigger by compressive stresses induced in the PIIS by the SW Tributary Glacier.

Another possible factor in the collapse is the thinning of the ice shelf.
Those cracks parallel to the flow probably happened along grooves carved by warmer water flowing out of the cavity under the shelf. This event shows that the grooves are now deep enough to be significant weak points in the ice shelf. We may be entering a new era in the PIIS evolution.
Title: Re: PIG has calved
Post by: AbruptSLR on July 31, 2015, 05:25:22 PM
I looks to me like this mode of this spectacular calving event was trigger by compressive stresses induced in the PIIS by the SW Tributary Glacier.

Another possible factor in the collapse is the thinning of the ice shelf.
Those cracks parallel to the flow probably happened along grooves carved by warmer water flowing out of the cavity under the shelf. This event shows that the grooves are now deep enough to be significant weak points in the ice shelf. We may be entering a new era in the PIIS evolution.

Excellent points, and I expect the new splitting tension crack that A-team discusses will likely result in another major calving event within two years or less, and a repetition of this mechanism will progressive move the PIIS calving face upstream, thus progressively relieving buttressing from the SW Tributary Glacier which will progressive induce the adjoining Thwaites Glacier ice flow velocities to accelerate.
Title: Re: PIG has calved
Post by: crandles on July 31, 2015, 05:45:55 PM
I expect the new splitting tension crack that A-team discusses will likely result in another major calving event within two years or less, and a repetition of this mechanism will progressive move the PIIS calving face upstream, thus progressively relieving buttressing from the SW Tributary Glacier which will progressive induce the adjoining Thwaites Glacier ice flow velocities to accelerate.

It seems to me the 2013 calving happened at the point where the northern end of that crack reached almost exactly the same point as the northern end of the latest crack has just reached.

See
http://www.bbc.co.uk/news/science-environment-23249909 (http://www.bbc.co.uk/news/science-environment-23249909)
(linked in first post of this thread)

Is the buttressing from the rock at the northern side the critical point, and wouldn't that continue for a while possibly with thinner glacier possibly moving faster and calving more frequently but at the same point?

(Note I probably don't know what I am talking about and could easily be misjudging the position to be about the same.)


Title: Re: PIG has calved
Post by: A-Team on July 31, 2015, 06:03:59 PM
It seems to me the 2013 calving happened at the point where the northern end of that crack reached almost exactly the same point as the northern end of the latest crack has just reached.

That would be just like Petermann Glacier which is pinned by rock walls and deflected tributaries instead of other glaciers.

Antarctica is a really big place -- here is thecorrect bounding box at Sentinel for Pine Island Glacier. This will pull out the files that Wipneus used for the animation above. (So many disintegrating ice shelves, so little time.) I found a slightly more recent 28 July scene that is GRDM EW (medium resolution, extra wide) rather than being the IW series. It will have distorted geometry and so cannot be easily added as an animation frame.

I added the rift two years up the road at full IW resolution (which does not add that much detail).

S1A_EW_GRDM_1SSH_20150728T032153_20150728T032257_007005_009832_866D
Title: Re: PIG has calved
Post by: AbruptSLR on July 31, 2015, 06:29:46 PM
I expect the new splitting tension crack that A-team discusses will likely result in another major calving event within two years or less, and a repetition of this mechanism will progressive move the PIIS calving face upstream, thus progressively relieving buttressing from the SW Tributary Glacier which will progressive induce the adjoining Thwaites Glacier ice flow velocities to accelerate.

It seems to me the 2013 calving happened at the point where the northern end of that crack reached almost exactly the same point as the northern end of the latest crack has just reached.

See
http://www.bbc.co.uk/news/science-environment-23249909 (http://www.bbc.co.uk/news/science-environment-23249909)
(linked in first post of this thread)

Is the buttressing from the rock at the northern side the critical point, and wouldn't that continue for a while possibly with thinner glacier possibly moving faster and calving more frequently but at the same point?

(Note I probably don't know what I am talking about and could easily be misjudging the position to be about the same.)

From a fracture mechanics point of view the pre-existing crevasses and basal meltwater channel patterns are critical (together with other boundary conditions, ice thickness and shelf location & geometry) for determining whether the failure mechanism will hinge about the north or south end of the splitting tension crack.  I suspect that the 2013 calving event swung out at the north end because local cracking around the submerged pinnacle allowed it to swing free there; while I suspect that this 2015 event has the calving face located further upstream than the 2013 event, so that the lateral (downstream) kicking force was stronger, and as Yuha points out there were likely sufficient pre-existing basal grooves (or channels) cut in the bottom of the ice shelf to allow a wedge shaped iceberg to be kicked out (also pushing the southern iceberg ahead of it).

As the calving face moves still further upstream, we may see different variations of calving events that are slightly different than both the 2013 & 2015 event but also with many commonalities.

Certainly, the PIIS is becoming thinner, and with the El Nino should have more subglacial meltwater grooves (channels); so for some decades to come we can certainly expect major calving events to me more frequent.
Title: Re: PIG has calved
Post by: oren on August 01, 2015, 01:47:49 AM
Thanks to all those that responded to my rather stupid question. It all clicked into place.
Title: Re: PIG has calved
Post by: sidd on August 01, 2015, 05:14:26 AM
the name of this thread ought to have " again" at the end. I am sure people will be discussing this for a few more years (until the discussion moves to "Thwaites has fallen in, run inland and upwards")

sidd
Title: Re: PIG has calved
Post by: oren on August 01, 2015, 09:34:23 AM
Is it possible to compare the calving front position to the position after the previous major calving? I'm wondering if there's a retreat or not.
Title: Re: PIG has calved
Post by: solartim27 on August 02, 2015, 05:10:28 PM
Just a glimpse of the notch area today.  Rotation around the pinnacle is evident.
Title: Re: PIG has calved
Post by: AbruptSLR on August 03, 2015, 01:46:28 AM
Just a glimpse of the notch area today.  Rotation around the pinnacle is evident.

solartim27,

Another nice catch.  This image shows that the western face of the pinned iceberg clearly follows the alignment of the old splitting tension crack.  It will be interesting to see how long it takes for this iceberg to un-pin itself.

Best,
ASLR
Title: Re: PIG has calved
Post by: Wipneus on August 03, 2015, 02:23:28 PM

Do you have earlier frames handy? To date the new crack, see when it developed, whether it is progressing. Also one longitudinal crack, bottom left, seems to pre-date the horizontal developments.


Sorry I missed this question at first. These are the PIG files that I have:

S1A_IW_GRDH_1SSH_20141009T084630_20141009T084655_002750_003169_F84D.zip
S1A_IW_GRDH_1SSH_20141010T043522_20141010T043546_002762_0031AF_F034.zip
S1A_IW_GRDH_1SSH_20141022T043522_20141022T043547_002937_00355B_95D6.zip
S1A_IW_GRDH_1SSH_20150207T043519_20150207T043544_004512_0058A1_FEB5.zip
S1A_IW_GRDH_1SSH_20150219T043519_20150219T043544_004687_005CB0_749C.zip
S1A_IW_GRDH_1SSH_20150408T043519_20150408T043544_005387_006D8A_7DC3.zip
S1A_IW_GRDH_1SSH_20150420T043520_20150420T043545_005562_0071E3_5E98.zip
S1A_IW_GRDH_1SSH_20150502T043521_20150502T043546_005737_0075DF_DC8B.zip
S1A_IW_GRDH_1SSH_20150526T043535_20150526T043600_006087_007E31_01D2.zip
S1A_IW_GRDH_1SSH_20150619T043537_20150619T043602_006437_00883B_D089.zip
S1A_IW_GRDH_1SSH_20150701T043537_20150701T043602_006612_008D15_C99D.zip
S1A_IW_GRDH_1SSH_20150713T043524_20150713T043549_006787_0091F9_7479.zip
S1A_IW_GRDH_1SSH_20150725T043525_20150725T043550_006962_0096F9_D8D7.zip


On the new crack: I noticed that for the first time on a Landsat image from 6th Feb. Seen it since then both Landsat and Sentinel images, developing from a "maybe" to certainly in these latter images.
http://forum.arctic-sea-ice.net/index.php/topic,429.msg44967.html#msg44967 (http://forum.arctic-sea-ice.net/index.php/topic,429.msg44967.html#msg44967)
Title: Re: PIG has calved
Post by: A-Team on August 03, 2015, 05:03:08 PM
Thanks! The second crack you observed back in February is just barely visible in the 01 Dec 14 Landsat (after beating on it with local adaptive contrast).
Title: Re: PIG has calved
Post by: Wipneus on August 08, 2015, 03:31:16 PM
Sequence of two frames, each a combination of two hi-res (IW) Sentinel images, shows the before and after of the recent calving.
Title: Re: PIG has calved
Post by: crandles on August 08, 2015, 03:55:39 PM
Is it possible to rotate, scale and align and create blink gif of

http://ichef-1.bbci.co.uk/news/624/media/images/68649000/jpg/_68649121_2013_07_02.jpg (http://ichef-1.bbci.co.uk/news/624/media/images/68649000/jpg/_68649121_2013_07_02.jpg)

to show where the current calving front on last gif is compared to last time?

Or is this impossible? Too few points not on glacier that are too uncertain as to position on other image? (There seem to be a couple of clearly recognisable features on the south side of the glacier.)
Title: Re: PIG has calved
Post by: AbruptSLR on August 08, 2015, 05:37:19 PM
While I have not developed very good image processing skills, the attached image by Matt Owens, compares the PIIS condition in Sept 2012 to Sept 2013.  When one compares this image with the blink images Wipneus just posted of the PIIS in July - August 2015 it is apparent how far upstream the calving face has migrated.  While the face migration associated with the July 2015 calving leaves substantial buttressing support for the SW Tributary Glacial; I would not be surprised if the next upstream splitting tension (and/or flexural) crack will likely calve still further upstream (particularly because of the active advection of warm CDW currently occurring below the PIIS); which will likely further reduce the buttressing support on the SW Tributary Glacier.
Title: Re: PIG has calved
Post by: Wipneus on August 08, 2015, 07:01:04 PM
Is it possible to rotate, scale and align and create blink gif of

http://ichef-1.bbci.co.uk/news/624/media/images/68649000/jpg/_68649121_2013_07_02.jpg (http://ichef-1.bbci.co.uk/news/624/media/images/68649000/jpg/_68649121_2013_07_02.jpg)

to show where the current calving front on last gif is compared to last time?

Or is this impossible? Too few points not on glacier that are too uncertain as to position on other image? (There seem to be a couple of clearly recognisable features on the south side of the glacier.)

Could be better, but here is something.
Title: Re: PIG has calved
Post by: oren on August 08, 2015, 07:06:38 PM
Wow. What a difference over two years. I was working on some comparison, but my gimp is misbehaving and my skills are low.
It's interesting that the whole retreat is on one side of the flow, I guess this has to do with the pressure from the SW tributary glacier (or maybe something with the flow of warm water underneath).
Title: Re: PIG has calved
Post by: crandles on August 08, 2015, 08:31:54 PM
Thank you very much. Large retreat on south side was evident, but trying to rotate in my head to try to figure out how much  the north side had retreated and any changes on north side buttressing was beyond me.
Title: Re: PIG has calved
Post by: AbruptSLR on August 08, 2015, 08:42:55 PM
Thank you very much. Large retreat on south side was evident, but trying to rotate in my head to try to figure out how much  the north side had retreated and any changes on north side buttressing was beyond me.

The large retreat is on the north side.

Edit: I forgot to say how awesome Wipneus' images are.
Title: Re: PIG has calved
Post by: solartim27 on August 08, 2015, 08:44:33 PM
It's interesting that the whole retreat is on one side of the flow, I guess this has to do with the pressure from the SW tributary glacier (or maybe something with the flow of warm water underneath).
The first flow in the 2013 picture caused the start of this thread (I think).  The part that is still remaining can be seen upstream of the crack in the 2013 picture, and is grounded on an undersea pinnacle.

I am curious about the new cracks forming, and how long it takes for the next calving event.  Does anyone have the dates for noticing the crack for the 2013 calving?  The current calving was first seen in a post by Wipneus in Oct 2014, and calved several months earlier than AbuptSLR's prediction.

The next crack is visible in this shot from June, but I don't know if that is the earliest
Title: Re: PIG has calved
Post by: AbruptSLR on August 08, 2015, 11:44:05 PM
So that others can learn from my mistakes:  In my opinion the primary reasons that my "prediction" of the calving event was off by several months are: (a) I assumed that sea ice would pin the pending iceberg in place longer; however, the strong current El Nino appears to have advected so much warm CDW into the area that the local sea ice looks either fragile or absent; and (b) I had not accurately considered how the basal melting and associated basal changes would allow the pending iceberg to fracture into so many pieces (i.e. while the primary rupture was along the blue line in the first attached image from Reply #221, the secondary along the red line drawn by icefest in Reply #207, came as a surprise to me).

On to projecting the next major calving event: In my opinion the July 2015 calving event has changed the compressive stress field in the PIIS due to the SW Tributary Glacier (see the second attached image from MacGregor 2012); which, leads me to suspect that before any new major calving event occurs we will see a new splitting tension (flexural) crack upstream from the crack highlighted in A-Team's animation in Reply #357.  I believe that this new crack will line-up with the arrow marked "A" in the third attached image by icefest in Reply 217 (note to crandles: the longitude & latitude lines on this image show help you to get out of your NH orientation & into a SH orientation) and that within ½ year of the formation of this new crack formation (say by January 2016) that the new major calving will occur along the crack highlighted by A-Team in Reply #357; which more or less means that I am "predicting" another major calving event in next year's July-August timeframe.  If this occurs, the buttressing on the SW Tributary Glacier will be further reduced.

P.S.: Note that the change in the direction for ice flow in the MacGregor image is due to the compressive stress between the SW Tributary Glacier & the PIIS; and that as the buttresses action of the PIIS progressively degrades in the coming decade, or two, the ice flow direction of the SW Tributary Glacier ice will progressive change to point more upstream.  Thus future splitting tension (flexural) crack will likely migrate upstream from point "A" (at Evans Knoll) in the third attached image, progressively to points further upstream.
Title: Re: PIG has calved
Post by: Wipneus on August 09, 2015, 02:07:07 PM
Here is a different comparison between 2013 and 2015, this time with Landsat 7/8 thermal images. For the Landsat 7 2013 image that is band 6V1, for the Landsat 8 2015 I used band 10.
The 2013 crack is clear without image enhancement. To bring out the 2015 crack I manipulated the contrast somewhat.
Title: Re: PIG has calved
Post by: solartim27 on August 12, 2015, 06:07:18 AM
Do we need a new thread for Thwaites? 

Sentinel went by again, and I noticed some movement.  I have no idea how this motion compares for ZI or JI up in Greenland, but since PIG remnants show up it's valid to go here.  Here is a GIF from 8/1 to 8/11, and the overview of the area.
Title: Re: PIG has calved
Post by: Wipneus on August 23, 2015, 06:42:01 PM
The Sentinel image from the 18th shows that the grounded calving split in two.

(click to animate)
Title: Re: PIG has calved
Post by: solartim27 on August 23, 2015, 06:48:10 PM
Do you see a new crack forming above the old new crack, or is my screen dirty?
Title: Re: PIG has calved
Post by: AbruptSLR on August 23, 2015, 07:22:33 PM
Do you see a new crack forming above the old new crack, or is my screen dirty?

First, I would like to thank Wipneus again for providing such outstanding images.

That said:
(a) While I do not yet see a new crack forming upstream of the old new crack; it does appear to me that the old new crack is extending to the southwest, and I am concerned that when the calving front collides with the still grounded iceberg that the new old crack will extend still further to the southwest.
(b) I remark on how little sea ice there is in this area, suggesting that the advection of warm CDW is high at the moment (probably due to the strong and strengthening current El Nino event); and I am concerned that such abnormally strong advection of warm CDW is accelerating basal melting of the ice shelf, and may have contributed to the fracturing of the grounded iceberg.
(c) I am further concerned that if the "old new crack" extends far enough to the southwest then the next major calving event of the ice down stream of the "old new crack" may occur (maybe a year from now) when an ice fracture occurs in the middle of the calving front and normal to the calving face so as to form two new icebergs that can rotate outward from such a hypothetical rupture (normal to the calving front) by pivoting about the northeast and southwest corners of the ice front.
Title: Re: PIG has calved
Post by: icefest on August 24, 2015, 09:55:39 AM
Do you see a new crack forming above the old new crack, or is my screen dirty?

Do you mean A or B?

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2FjMwt7%2F04174853d5.jpg&hash=00b80a5cb9717094218bfedf06d26bd1)
Title: Re: PIG has calved
Post by: AbruptSLR on August 24, 2015, 11:15:13 AM
Reply #371 was referring to "A" as the "old new crack".
Title: Re: PIG has calved
Post by: solartim27 on August 24, 2015, 09:14:45 PM
I circled the area I was referring to.  Sorry for the confusion, should have done that first.
Title: Re: PIG has calved
Post by: AbruptSLR on August 25, 2015, 12:52:32 AM
I circled the area I was referring to.  Sorry for the confusion, should have done that first.

Right, or wrong, I do not yet see any crack in the area that solartim27 circled; however, I imagine (based on my understanding of fracture mechanics) that by this austral summer will we likely see a crack immediately upstream of this circled area.  Further, I image that by the July-August 2016 timeframe a new calving event will occur along the crack labeled A.
Title: Re: PIG has calved
Post by: anotheramethyst on August 25, 2015, 07:53:45 AM
I circled the area I was referring to.  Sorry for the confusion, should have done that first.

i see it too.  i had to zoom in all the way to see it, and it's clearest on the far right and far left edges, in the middle it seems to disappear completely.  its so faint i would want to see another pic of it to confirm it.... but solartim ur screen cant possibly be dirty!!!! (maybe we both have the contrast settings too high? :) haha just kidding)
Title: Re: PIG has calved
Post by: AbruptSLR on August 26, 2015, 04:24:27 PM
The attached Sentinel 1a image of the northeast corner of the PIIS from August 25 2015 shows: (a) minor calving in the "notch" area, and (b) that the calving face of the PIIS is about to contact the grounded iceberg.
Title: Re: PIG has calved
Post by: solartim27 on August 28, 2015, 11:07:23 PM
The sun has returned so I made a GIF with Sep 14, 2014.  Sort of cloudy, so it's hard to pick a good spot to compare the amount of advancement.  Looks like the calving in the notch has continued, filling in the open water behind the stuck berg.

EDIT:  You can see marks showing a big advance of the southwest (?) tributary glacier, It has been slowly moving over the year, comparing the Sep 14 pic with Apr 1, 2015, but it doesn't look like it has picked up speed since the last PIG calving.
Title: Re: PIG has calved
Post by: solartim27 on August 28, 2015, 11:40:26 PM
I zoomed in on the southwest tributary glacier, and added the Apr 1 frame.
Title: Re: PIG has calved
Post by: AbruptSLR on August 29, 2015, 12:39:51 AM
I zoomed in on the southwest tributary glacier, and added the Apr 1 frame.

Thanks for the great detective work on the SW Tributary Glacier showing that it has not yet significantly accelerated due to loss of buttressing.
Title: Re: PIG has calved
Post by: solartim27 on August 29, 2015, 01:26:38 AM
I wish I was as confident as you make me sound.  I think it's too soon after the break to say for sure, and I don't think Modis gives a good enough resolution to say for sure.

It's going to be an interesting austral summer.  Wonder if we'll see melt ponds anywhere, that would be something.
Title: Re: PIG has calved
Post by: AbruptSLR on August 29, 2015, 01:42:40 AM
I wish I was as confident as you make me sound.  I think it's too soon after the break to say for sure, and I don't think Modis gives a good enough resolution to say for sure.

It's going to be an interesting austral summer.  Wonder if we'll see melt ponds anywhere, that would be something.

Here is a photo of melt ponds on PIIS circa 2005:
Title: Re: PIG has calved
Post by: Wipneus on August 31, 2015, 11:02:43 AM
A new hi-res (IW) image, here rendered at 30m/pix from sentinel is available. The free floating calving has moved out, the grounded part will meet with the glacier soon. Perhaps when the Sentinel is again in the same orbital position: 11th September.

(must click)
Title: Re: PIG has calved
Post by: AbruptSLR on September 02, 2015, 05:16:25 PM
For fun I post both the Terra and the Aqua satellite images, respectively, of the PIIS for Sept. 1 2015.  And while it is too cloudy to say for sure, it appears that a limited amount of minor calving is occurring on the calving face near the notch area (northwest end of the calving front), but otherwise, very little change is indicated in the pinned iceberg.
Title: Re: PIG has calved
Post by: solartim27 on September 03, 2015, 11:24:03 PM
Looks to me like the pinned berg has broken apart, hard to say for sure.
Edit:  Still there on the Aqua image.
Title: Re: PIG has calved
Post by: AbruptSLR on September 06, 2015, 08:26:21 PM
I post the two accompanying Terra images both from Sept 5 2015 to show that: (a) the first image shows that the iceberg in front of the PIIS is still grounded and (b) the second image shows that the icebergs that moved away from the PIIS calving front are now locked in sea ice, as is the Thwaites Ice Shelf and residual Ice Tongue.
Title: Re: PIG has calved
Post by: AbruptSLR on September 11, 2015, 05:26:57 PM
In the way of an update.  The attached image of the PIIS is by Aqua from the afternoon of September 10 2015, and to me it indicates that the fractured ice field from the "notch" area appears to be in compression now and may be pushing the grounded iceberg, thus preventing the rest of the calving front from making contact with the berg.  If so, this may: (a) slow and/or prevent the reformation of the "notch" until the grounded iceberg is displaced; and (b) increase the span-length contributing to accelerated splitting tension crack extension as the season progresses.
Title: Re: PIG has calved
Post by: Wipneus on September 11, 2015, 07:09:27 PM
The once in 12-day Sentinel 1A update. The grounded calving manages to slide somewhat with the approaching glacier front, keeping the gap still open.

(click to animate)
Title: Re: PIG has calved
Post by: AbruptSLR on September 13, 2015, 05:08:00 PM
While I cannot say for sure, the first attached Aqua image from the afternoon of Sept 12 2015 appears to indicate that the northeastern portion of the grounded iceberg may be fracturing/calving (or this appearance could be the influence of clouds, and/or confusion with sea ice). The second image shows the same photograph with blue contrasts that help to show where the clouds end and the ice begins.
Title: Re: PIG has calved
Post by: AbruptSLR on September 16, 2015, 12:03:29 AM
The attached Terra image from Sept 15 2015, makes it clear that the grounded iceberg near the PIIS calving front is still intact.
Title: Re: PIG has calved
Post by: Wipneus on September 19, 2015, 08:57:16 AM
Landsat season has started!

Here is the first reasonably unclouded image of the southern summer. The width of the split between the grounded calving and the glacier is less than 60m wide.
To my surprise in this mostly untreated image the new crack is NOT visible. Snow? fog? Call in A-team for torturing some data?

(click the picture for a 60m/pix image)
Title: Re: PIG has calved
Post by: Wipneus on September 19, 2015, 02:56:26 PM
Comparing with last season's images and applying judicious contrast enhancements brings out the future crack running top-left to bottom-right in the second attached image.
Title: Re: PIG has calved
Post by: AbruptSLR on September 19, 2015, 07:33:29 PM
Comparing with last season's images and applying judicious contrast enhancements brings out the future crack running top-left to bottom-right in the second attached image.

Wipneus,

Thanks for the great images.  It looks to me like the crack/crevasse is likely buried by some recent snowfall.  Also, if you have a chance sometime, could you try to estimate the ice flow speed for the small "Southwest Tributary Glacier" Ice Shelf that is immediately located to the southwest of the PIIS.  While I do not think that this ice flow speed has accelerated yet, it would be nice to have a baseline speed to compare to, should the PIIS calving front retreat far enough in the next few years for the Southwest Tributary Glacier flow speeds to accelerate.

Best,
ASLR

Edit: See Reply #379
Title: Re: PIG has calved
Post by: A-Team on September 20, 2015, 02:25:26 PM
Snow? fog? Call in A-team for torturing some data? injudicious contrast enhancements to bring out the crack? buried by some recent snowfall?

I could envision blowing old snow, new snow, or the sun not oriented favorably for crack shadowing (eg, along-crack). While reflectance of incident radiation will vary greatly with wavelength, it is most unusual in Greenland for Sentinel radar to provide better resolution of ground features than cloud-free Landsat.

This is not snow-penetrating radar and a 15 m wide crack would not induce noteworthy polarization effects so it's not clear why Sentinel would see any better under the first two scenarios. However Sentinel sweeps a forward-looking oblique view whereas Landsat looks straight down (nadar view). Only the former sees terrain shadowing (crack depression by edge of crack).

I don't have the Sentinel orbital metadata handy but being in polar orbit, it presumably crosses the image at a slight angle to north-south. This would give it some terrain shadowing of the track because it has a goodly east-west component. It's always a good idea to draw a line on in the image showing the orbital track if there has been re-projection.

Meanwhile, metadata on the 18 Sep 15 Landsat above (LC82321132015261LGN00) shows fairly extreme sun elevation and azimuth. As indicated in the second image below, Landsats at EarthExplorer arrive re-projected to a local Mercator patch with north still up for Antarctica.

Sun Elevation     6.4º
Sun Azimuth    57.6º

Such a low sun angle is normally extremely favorable for showing slight variations in landscape elevation but here the odd azimuth may undo that benefit by more or less aligning with the crack, causing it not to be shadowed. Here the operative azimuthal convention has 180º due south. This makes it much harder to tweak contrast usefully while at the same time not introducing artifacts (first image).

The crack is barely visible in minimally enhanced band 8 of this Landsat (equilization). It can be drawn out somewhat by an adaptive contrast enhancement series, and perhaps more with a northeasterly shadowing convolution or embossing/bump map step. Note the azimuthal shadowing direction is quite apparent in the ridging.
Title: Re: PIG has calved
Post by: solartim27 on September 20, 2015, 08:24:30 PM
There was a sentinel shot over part of the area, so I wanted to look at what I had called the 'new new crack' above.  On a whim I tried an image enhancement, here is the result in a gif.  I believe it is the grounding line we are looking at, as it can be seen to extend clearly past the area I had circled.  Could it be that a combination of glacier advancement with extreme tidal fluctuations is what results in the ridges and cracks?

You'll need to click the lower image to see the enhanced image gif.

Edit, added the enhanced still image.
Title: Re: PIG has calved
Post by: AbruptSLR on September 22, 2015, 09:14:42 PM
solartime27,

If you are correct, then the images that you show may indicate that the "new new crack" extends all the way to the northeast side of the PIIS.

Separately,

Attached is a relatively clear Terra image for Sept 22 2015, showing that the main calving front is about to make contact with the grounded iceberg.

Best,
ASLR
Title: Re: PIG has calved
Post by: Lennart van der Linde on September 25, 2015, 08:31:22 AM
Mauri Pelto on new PIG-calving:
http://blogs.agu.org/fromaglaciersperspective/2015/09/24/pine-island-releases-new-iceberg-after-austral-winter-2015/ (http://blogs.agu.org/fromaglaciersperspective/2015/09/24/pine-island-releases-new-iceberg-after-austral-winter-2015/)
Title: Re: PIG has calved
Post by: nukefix on September 25, 2015, 05:07:29 PM
SAR penetrates deep into a dry snowpack, at C-band we are talking meters of even tens of meters.
Title: Re: PIG has calved
Post by: Wipneus on September 26, 2015, 01:40:46 PM
This latest Landsat image, natural color pan-sharpened to 15m/pixel, shows that the gap between glacier en grounded calving has about closed. The very bright stuff near the "contact spot" may be the result of the collision.
Title: Re: PIG has calved
Post by: AbruptSLR on September 29, 2015, 05:29:03 PM
The two attached images were taken by the Sentinel 1a on Sept 26 2015.  The first image shows that the ice shelf for the Southwest Tributary Glacier is continuing to grow (possibly, or not, at an accelerated rate compared to that before the most recent PIIS major calving in July 2015).  The second image shows that the grounded iceberg at the seaward end of the residual Thwaites Ice Tongue is moving northward faster than the Thwaites Eastern Ice Shelf, which raises the prospect that this iceberg might re-float as soon as this austral summer (which could then increase the rate of the local Thwaites ice flow).
Title: Re: PIG has calved
Post by: Wipneus on October 12, 2015, 10:50:35 AM
Many cloudy days over the PIG calving front. In this sequence with an image where the clouds are thin enough to see that the grounded ice berg, now in contact with the glacier, is moving now with the said glacier. A very small calving from the glacier can be seen in the corner.

(click to animate)
Title: Re: PIG has calved
Post by: Wipneus on November 13, 2015, 01:39:40 PM
Sentinel 1A image fro 11th November. The events near the calving front continue, but slowly. The grounded calving is moving with the glacier front, new cracks are getting slowly wider and longer.

This time a zoom-in much higher upstream, near the top of this full Sentinel image (first attachment).

Zooming in to 50m/pix  (second attachment, click to enlarge) reveals a striking pattern made from fine lines: lanes of parallel lines that are  crossing other lanes in places.

Further zooming in to 10m/pix in attachment three makes an image that looks more like a part of hair-dress than that of a glacier.
Title: Re: PIG has calved
Post by: A-Team on November 13, 2015, 04:22:42 PM
Amazing. Was this known? I see now where you are zooming in relative to the first image at the funnel narrowing, though the lineation zone continues quite a ways. The second image should be opened to its full (unchanged) 50 m resolution. What is the counterpart in Landsat-8?
Title: Re: PIG has calved
Post by: crandles on November 13, 2015, 05:03:47 PM
Fascinating. With a funnel reducing width of an ice stream I would have expected any patterns to be very jumbled up. Instead lots of thin parallel lines that are reasonably straight stretching most of way across the ice stream. How does that work?
Title: Re: PIG has calved
Post by: plinius on November 13, 2015, 07:45:37 PM
If the fracture propagates upstream and each fracture covers preferably the full width (tick, that's also true for such a glacier), that's a quite likely pattern. Also, you see some "jumbling", where lines are at an angle to open into the arch. But they cannot easily cross, since a fracture stops a propagating fracture trying to cross it.
Title: Re: PIG has calved
Post by: AbruptSLR on November 13, 2015, 08:20:59 PM
Zooming in to 50m/pix  (second attachment, click to enlarge) reveals a striking pattern made from fine lines: lanes of parallel lines that are  crossing other lanes in places.

As plinius points out, the "lines" are snow covered crevasses and, at places, they are not crossing each other but rather are intersecting each other.  In this regards the two attached images illustrate the geometries of transverse, marginal, longitudinal and radial splaying crevasses in a glacier.

Edit: I note that some crevasses only extend down from the upper surface and some crevasses only extend up from the basal surface, while some crevasses extend all the way through the glacier.  Furthermore, some crevasses can heal themselves with time and exposure to water within the crevasse, thus the PIIS calves in a distinctly different manner than say the Jakobshavn Glacier, as Jakobshavn's cervasses do not have much time to heal before calving, while the PIIS is more coherent and thus can calve much larger icebergs.
Title: Re: PIG has calved
Post by: A-Team on November 13, 2015, 10:53:24 PM
Do we have a surface velocity overlay? Hill-shaded surface relief? Bedrock surface? That is, from the wavelength of crevassing and curvature going from convex to flat to concave, what could we have deduced?
Title: Re: PIG has calved
Post by: AbruptSLR on November 14, 2015, 12:09:56 AM
Do we have a surface velocity overlay? Hill-shaded surface relief? Bedrock surface? That is, from the wavelength of crevassing and curvature going from convex to flat to concave, what could we have deduced?


Maybe you can extract some information from the following Rignot paper and the attached images:

http://www.ess.uci.edu/researchgrp/erignot/files/grl51433.pdf (http://www.ess.uci.edu/researchgrp/erignot/files/grl51433.pdf)
Title: Re: PIG has calved
Post by: A-Team on November 14, 2015, 04:39:16 PM
Why does this remind me more of viscous buckling rather than crevassing? I am still looking for Landsat imagery covering something else than the ice shelf and area immediately above. The km scale of Antarctica discourages anything more. 

I am downloading LIMAs of this region right now. Actually it is quite difficult to say if the image snippet below really covers the same turf as the Sentinel. The Landsat Image Mosaic of Antarctica (LIMA) is seamless and virtually cloudless and pan-sharpened but seemingly Landsat-7 from eight years back. http://lima.usgs.gov/access.php (http://lima.usgs.gov/access.php) 

We need to tweak nukefix's Sentinel Toolbox diagram to put those images in polar stereographic like Landsat-8 below -63º latitude.

Lava Flows and Folds. When lava flows, the outside layer quickly cools forming an exterior crust. In fact, many of the lava patterns we found were quite thin and hollow inside where the lava had subsequently evacuated after the structures were formed. This cooled layer is significantly more viscous than the lava below acting like a viscous sheet. Folds begin to form when the flow compresses due to the slowing of the flow front. This compression could be caused by hitting an obstruction or entering a narrow channel. These folds form in the span of seconds to minutes.

The folding of viscous or elastoviscous materials has been widely studied recently both in physical experiments with non-Newtonian fluids and numerical simulations. Pahoehoe lava forms exhibit relatively regular fold properties; their folds form perpendicular to the direction of flow with a consistent wavelength and amplitude. This property is shown very purely in examples of viscous sheets. Check out the videos below. One shows the buckling of pancake batter being poured into a pan...  http://tinyurl.com/qyd4sb6 (http://tinyurl.com/qyd4sb6)
Title: Re: PIG has calved
Post by: A-Team on November 14, 2015, 04:46:50 PM
Before i misplace this December 2000 photo taken with an interesting triple camera technique ...

This pair of Multi-angle Imaging Spectroradiometer (MISR) images of the Pine Island Glacier in western Antarctica was acquired on December 12, 2000 during Terra orbit 5246. At left is a conventional, true-color image from the downward-looking (nadir) camera.

The false-color image at right is a composite of red band data taken by the MISR forward 60-degree, nadir, and aftward 60-degree cameras, displayed in red, green, and blue colors, respectively. Color variations in the left (true-color) image highlight spectral differences. In the multi-angle composite, on the other hand, color variations act as a proxy for differences in the angular reflectance properties of the scene.

In this representation, clouds show up as light purple. Blue to orange gradations on the surface indicate a transition in ice texture from smooth to rough. For example, the bright orange 'carrot-like' features are rough crevasses on the glacier's tongue. In the conventional nadir view, the blue ice labeled 'rough crevasses' and 'smooth blue ice' exhibit similar coloration, but the multi-angle composite reveals their different textures, with the smoother ice appearing dark purple instead of orange. This could be an indicator of different mechanisms by which this ice is exposed. The multi-angle view also reveals subtle roughness variations on the frozen sea ice between the glacier and the open water in Pine Island Bay.
http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=1300 (http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=1300)
Title: Re: PIG has calved
Post by: Wipneus on November 15, 2015, 09:14:16 AM

We need to tweak nukefix's Sentinel Toolbox diagram to put those images in polar stereographic like Landsat-8 below -63º latitude.


Or with gdalwarp:

gdalwarp -t_srs 'EPSG:3031' -tr 15 15  s1a-iw-grd-hh-20151110t043528-20151110t043553-008537-00c17b-001.tiff s1a-iw-grd-hh-20151110t043528-20151110t043553-008537-00c17b-001-polar.tiff

(the -tr option specifies the target resolution)
Title: Re: PIG has calved
Post by: Wipneus on November 15, 2015, 09:50:43 AM
Here is a detail, comparing a Landsat image (from 2015-03-05) with the re-projected (see above) Sentinel image.
It is cool that the snow penetrating Sentinel imagery is superior to Landsat optical on showing these features.
Title: Re: PIG has calved
Post by: A-Team on November 15, 2015, 01:03:57 PM
cool that the snow penetrating Sentinel imagery is superior to Landsat optical on showing these features.
The 05 Mar 2015 Landsat LC82291142015064LGN00 is a nice image and suited to displaying shadows at 11.9º sun elevation from azimuth 66.6º but if these features consist of windblown snow or undulations or crevasses filled in by snow, then Sentinel is way ahead. Snow doesn't get any drier than in central Antarctica which is favorable for radar penetration. Still, we are seeing a detailed optical surface counterpart.

The first image, Band 8 from the same Landsat, shows some context for the image posted above -- and the vast scale of these features. If the funnel area is a saddle or pass, there could be a venturi effect on the wind affecting snow deposition. There are regions that look 'overwritten' which would be consistent with a change in wind direction.

I looked at the 31 Oct 2015 Landsat LC82291142015304LGN00 because the next step here is to look at age, stability and motion of the features. If these are crevasses, I would expect a new one to emerge at the top of the line and the older ones to move down a few pixels to the sea.

However these images are not so easy to align (but see 4th image which is aligned centrally, there being no fixed ground control points) and it might be better to do the animation with more closely spaced Sentinel 50 m.

Nice work with gdal. I have not checked if Sentinel toolbox diagrams are as portable as gdal script.

I looked into auto-alignment of Landsats based on what pixels shifts it takes to match their lower left hand corners. Might be easier to determine the conversion factors empirically for polar stereographic in this neighborhood. (Seems like they should provide a tool for aligning any two overlapping pairs.)

064 CORNER_LL_LAT_PRODUCT = -74.53846
304 CORNER_LL_LAT_PRODUCT = -74.53599
064-304 LL corner diff  =  00.00247
.001º lat diff —> 111m*1pxl/15m = 7.4*2.47 = 18.3 pxl shift down pre-projection

CORNER_LL_PROJECTION_X_PRODUCT = -1659600
CORNER_LL_PROJECTION_Y_PRODUCT = -318000

CORNER_LL_PROJECTION_X_PRODUCT = -1659300
CORNER_LL_PROJECTION_Y_PRODUCT = -321000

diff CORNER_LL_PROJECTION_X_PRODUCT =  300
diff CORNER_LL_PROJECTION_Y_PRODUCT = 2000
Title: Re: PIG has calved
Post by: A-Team on November 15, 2015, 04:13:37 PM
Here are some oblique views of regional velocities, frame grabs from Nasa's scientific visualization center in nullschool mode. These might help locate our feature relative to the big five-way confluence. The 4th image may even be in Landsat-compatible polar stereographic projection -- it is from same J Mouginot that's first author on the new Zachariae article.

https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=3848

It's not at clear anyone has ever set foot on the area we are looking at as I don't think radar skidoos would come so far up-glacier.

https://en.wikipedia.org/wiki/Pine_Island_Glacier#History_of_fieldwork
Title: Re: PIG has calved
Post by: solartim27 on November 16, 2015, 07:20:55 AM
Small calving seen on the corner of PIG, but the shot from today is blurred, so it's hard to see how extensive it is.
Title: Re: PIG has calved
Post by: A-Team on November 16, 2015, 01:46:21 PM
Using ImageRaider, I located a better version of the Pine Island Glacier velocity magnitudes overlaid on elevation shaded relief (by J Mouginot). The second image expands on that and the third is a very rough overlay of Sentinel features. The fourth image shows the ice penetrating radar grid flown in 2014 overlaid on a typical bland radar scene.

In trying to align accurately to a map in unspecified projection, it boils down to four polar projections in everyday use for Antarctica (ie supported in open source Proj.4 library and ArcGIS). Mouginot very likely used polar stereographic as favored by NSIDC (equal area at 71º). However there is still the issue of rotating to the same central meridian (grid north) which for Sentinel or Landsat in PS is likely driven by image center.

www.winwaed.com/blog/2010/01/11/polar-maps-and-projections-part-1-overview/ (http://www.winwaed.com/blog/2010/01/11/polar-maps-and-projections-part-1-overview/)

To color the Sentinel lineations, the velocity map is decomposed to HSV, the V value grayscale replaced with a suitably rescaled and rotated lineation grayscale, the S saturation replaced by a neutral gray, and the new enchilada reconstituted as RGB with the embedded velocity color scale going along for the ride.

This only gives the general idea because there weren't any coordinates on the Sentinel and interior Antarctica is short on visible features serving as ground control points. However if you look at the shearing on the left side of the Landsat animation three posts back, it does seem to correspond to the axial asymmetry of the velocity field. The bedrock is rather bland in this whole area and the ice is fairly deep at ~1500 m so the main issues are the slope and narrow chute at the breakpoint of the slope.
Title: Re: PIG has calved
Post by: A-Team on November 16, 2015, 05:35:20 PM
The time series of these lineations is critical to understanding their origination, history and differential motion. The list below provides the available coverage in Landsat (which has worse resolution than Sentinel but goes farther back) and Sentinel 1A (which is never cloudy and has a very consistent 12 day return but only back to last October).

Some of the cloudy Landsats might still be usable depending on the exact area being considered. The ones shown are all path,row 229,114. In both sets, you can see the necessity for bulk background downloading, cropping, and initial registration.

The physical scale of Antarctica is such that you may wish to purchase a hyperwall-2 visualization system before continuing on with this forum.  ;)

http://eospso.nasa.gov/content/about-nasas-hyperwall (http://eospso.nasa.gov/content/about-nasas-hyperwall)
http://svs.gsfc.nasa.gov/cgi-bin/search.cgi?contentType=hw (http://svs.gsfc.nasa.gov/cgi-bin/search.cgi?contentType=hw)
http://eospso.gsfc.nasa.gov/sites/default/files/publications/Hyperwall_How_To.pdf (http://eospso.gsfc.nasa.gov/sites/default/files/publications/Hyperwall_How_To.pdf)

LC82291142015304LGN00   Center -75.90225, -97.04894   31 Oct 15 clear #422
LC82291142015272LGN00   Center -75.90227, -97.07236   29 Sep 15 cloudy
LC82291142015080LGN00   Center -75.90204, -96.91553   21 Mar 15 cloudy
LC82291142015064LGN00   Center -75.90201, -96.93470   05 Mar 15 clear
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S1A_IW_GRDH_1SSH_20151110    T043528_20151110    T043553_008537_00C17B_5BDF *Wipneus #402
S1A_IW_GRDH_1SSH_20151029    T043459_20151029    T043528_008362_00BCE0_E120
S1A_IW_GRDH_1SSH_20151017    T043528_20151017    T043553_008187_00B827_9B3D
S1A_IW_GRDH_1SSH_20151005    T043459_20151005    T043528_008012_00B370_4D2B
S1A_IW_GRDH_1SSH_20150923    T043528_20150923    T043553_007837_00AEB7_FA55
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S1A_IW_GRDH_1SSH_20150907    T050754_20150907    T050819_007604_00A881_0508
S1A_IW_GRDH_1SSH_20150829    T084610_20150829    T084635_007475_00A4F7_A880
S1A_IW_GRDH_1SSH_20150818    T043458_20150818    T043526_007312_00A091_D39D
S1A_IW_GRDH_1SSH_20150806    T043526_20150806    T043551_007137_009BCD_354C
S1A_IW_GRDH_1SSH_20150725    T043525_20150725    T043550_006962_0096F9_D8D7
S1A_IW_GRDH_1SSH_20150721    T050723_20150721    T050752_006904_00954B_08D5
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S1A_IW_GRDH_1SSH_20150420    T043520_20150420    T043545_005562_0071E3_5E98
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S1A_IW_GRDH_1SSH_20150114    T043519_20150114    T043544_004162_0050C4_2177
S1A_IW_GRDH_1SSH_20150110    T050717_20150110    T050746_004104_004F83_AD0A
S1A_IW_GRDH_1SSH_20141229    T050747_20141229    T050812_003929_004B8C_CDC6
S1A_IW_GRDH_1SSH_20141220    T084604_20141220    T084629_003800_00489C_AA1F
S1A_IW_GRDH_1SSH_20141209    T043452_20141209    T043521_003637_0044F1_EBFF
S1A_IW_GRDH_1SSH_20141127    T043521_20141127    T043546_003462_0040E0_1ECF
S1A_IW_GRDH_1SSH_20141123    T050719_20141123    T050748_003404_003F81_B77B
S1A_IW_GRDH_1SSH_20141111    T050748_20141111    T050813_003229_003BAA_CD9F
S1A_IW_GRDH_1SSH_20141102    T084605_20141102    T084630_003100_0038DD_AB01
S1A_IW_GRDH_1SSH_20141022    T043453_20141022    T043522_002937_00355B_6F01
S1A_IW_GRDH_1SSH_20141010    T043522_20141010    T043546_002762_0031AF_F034
Title: Re: PIG has calved
Post by: AbruptSLR on November 16, 2015, 07:46:05 PM
Per Wipneus' Reply #324 about the ice flow velocity of the PIIS:

"So my result would be reported as 12 +/-4 [m/day]."

For comparison with Rignot's first attached plot Wipneus's 2015 ice velocity is 4.38 +/- 1.46 km/yr.

Thus, we should all remember when looking at the excellent recent posts in this thread, that the PIG/PIIS is still accelerating, and that when comparing modeled ice velocity estimates from 2011 with satellite images from 2015, that some transitional adjustments need to be kept in mind
Also, changes in ice surface elevations have an important impact on crevasse patterns and the second attached image shows the Goddard (NASA) estimated ice surface elevation drop from 2002 to 2011 in the ASE.
Title: Re: PIG has calved
Post by: nukefix on November 16, 2015, 08:12:40 PM
I'd love to see CryoSat swath-processed results over PIG/Thwaites..there's an order of magnitude more measurement-ppoints than just the POCAs (Point Of Closest Approach) coming from standard InSAR-processing...
Title: Re: PIG has calved
Post by: AbruptSLR on November 16, 2015, 08:45:09 PM
I'd love to see CryoSat swath-processed results over PIG/Thwaites..there's an order of magnitude more measurement-ppoints than just the POCAs (Point Of Closest Approach) coming from standard InSAR-processing...

Here is an image (first attachment) of Cryosat2 data for the ASE through 2013:

Edit: The second attached image is an Envisat elevation change image through June 2012
Title: Re: PIG has calved
Post by: AbruptSLR on November 16, 2015, 09:55:59 PM
The two attached images show cryostat 2 elevation change data from 2014 focused on the Antarctic Peninsula; however, the first image also showing elevation changes on the back side of the PIG.  This data shows a marked acceleration of ice mass loss from the indicated areas of the Antarctic Peninsula beginning in 2009:

Science 22 May 2015:
Vol. 348 no. 6237 pp. 899-903DOI:10.1126/science.aaa5727

http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/CryoSat_detects_sudden_ice_loss_in_Southern_Antarctic_Peninsula (http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/CryoSat_detects_sudden_ice_loss_in_Southern_Antarctic_Peninsula)

http://www.esa.int/spaceinimages/Images/2014/08/Antarctic_peninsula_ice-sheet_change (http://www.esa.int/spaceinimages/Images/2014/08/Antarctic_peninsula_ice-sheet_change)

Title: Re: PIG has calved
Post by: A-Team on November 18, 2015, 01:02:40 PM
Pine Island is still accelerating, and that when comparing modeled ice velocity estimates from 2011 with satellite images from 2015, that some transitional adjustments need to be kept in mind
In #402, the second Sentinel image is posted at 50 m per pixel resolution which means the first image (scaled by wipneus to 700 pxl width to fit the blog) is at 375 m resolution. Following the A2 to A1 flowline used by Rignot's group in the above images, the upper lineation region under study is 164 km from the calving front. This area is at 79.4º S, 97.7ºW so a couple hundred km more distant from the pole than Petermann.

The velocity and height changes noted in the first image of #418 are thus barely measurable here. Note quite a few of the images above are using logarithmic color scales which greatly exaggerates the low end. Velocities directly measured in the fourth image in #413 are only 18 days old, no correction is needed.

The focus of that animation, in Lagrangian co-moving coordinates, is velocity differentials over the 240 day interval back to early March 2015: these are measurable but just barely at 15 m resolution. Change is quite slow this far back in the Antarctic interior.

While the trend in extensional forces is increasing mildly, so too is the trend in compressional forces as ice from the five tributaries exits through the common chute at slightly increasing speeds. The first image shows the velocity contours at issue here. The isotachs (lines of constant velocity) are a so-so fit to the lineations under study but at least arched in the same orientation.

No one has posted any evidence to date supporting an interpretation as crevasses (brittle surface fractures). It's possible however they've been previously evaluated in the interior of a paywalled journal. And surely the crew of Icebridge saw all this close up in flying the 2014 grid at 1500 m. (They don't appear to shoot oblique time-lapse forward video however.)

We are very familiar from Jakobshavn and Zachariae with how crevasses appear in both Landsat and Sentinel (ie differently from here); from sub 1 m Worldview imagery at Google Earth we know the complex over-written waves of lineations northeast (not part of) Jakobshavn Isbrae are not crevasses. The same can be said for the northwest wall of Petermann -- frozen pressure waves in the ice are not crevasses.

I've since added the earliest Landsat-8s of 13 Jan 2014 and 15 Dec 2014 which have better intrinisic lineation contrast than the SH winter scenes. This gives us a 654 day history of lineation origination and development. Landsat-7 is more challenging because of the lower bit depth and scan line malfunction.

Glaciers exhibit many types of periodic surface features in addition to crevasses. The first image below shows a different periodic pattern well to the north of the area we're considering (yellow arrows). Note too the peculiar streaks visible only in Landsat (orange arrows) appear to originate solely at lineations, then extend down-flow, seeming to cast shadows.

It is premature to hypothesize about what wipneus is seeing in #402 and #412 because we are still in the early stages of constructing our GIS stack and collecting basic information. These features may curious but they're important only as observational proxies --  it's coastal region developments that drive significant change at Pine Island (as AbruptSLR notes in posts above).

We've hardly begun analyzing streaks and striations. The third image below counts the first 201 striations along 44 km km of a flowline. They are very regularly spaced as you can see at a glance, or by plotting the dispersion of inter-dot distances, or from the power spectrum of the fourier transform. The arches oppose the flow, somewhat reminiscent of ice at Nares Strait.

Because of antiquated informatics practices in glaciology, each layer in the stack is a separate color and registration hassle and each stack in each region a separate ad hoc exercise. In other areas of science, this would all be available as a pre-compute or as online tool path. Here we've seen only baby steps in that direction like pansharpened Landsat AWS archives but nothing like G'MIC for GDAL. (See the 301 interactive tools at https://gmicol.greyc.fr/)

We very rarely see one-parameter data properly conveyed as grayscale and spend a lot of time trying recover it from crappy color journal graphics that often irrevocably flatten multiple layers. It's even rarer to see two-parameter data like velocity conveyed in separate grayscale channels (eg hue for magnitude, saturation for direction).

These separate channels  make up the layers in a GIS stack (which can be 16- or 32-bit as well as 8). It's much more intuitive and convenient to do mathematical operations within a graphics stack but these are fully equivalent to a stack of numerical Excel sheets. These suffice for 99% of what we see; for example the SAR velocity measurements above have only 450 m resolution which makes for a very small spreadsheet even over a million sq km, even in conjunction with a hundred other layers.
Title: Re: PIG has calved
Post by: P-maker on November 18, 2015, 04:26:57 PM
A-team,

with reference to your post #416 (image in lower right hand corner), I would suggest a simple interpretation of the features we are seeing:

From Webster’s Dictionary 1913

Berg´schrund`
n.   1.   (Phys. Geog.) The crevasse or series of crevasses, usually deep and often broad, frequently occurring near the head of a mountain glacier, about where the névé field joins the valley portion of the glacier.”

See picture of one here:
http://www.swisseduc.ch/glaciers/glossary/bergschrund-en.html (http://www.swisseduc.ch/glaciers/glossary/bergschrund-en.html)

and a whole series here:
http://pubs.usgs.gov/of/2004/1216/b/images/bergschrund.gif (http://pubs.usgs.gov/of/2004/1216/b/images/bergschrund.gif)

And here is another (but very similar) definition:

Bergschrund, (German: “mountain crevice”), a crevasse or series of crevasses often found near the head of a mountain glacier. The erosion of the rock beneath a bergschrund contributes to the formation of a cirque, or natural amphitheatre.”

Which could indicate that the PIG has started to slide down the slope now and is eroding the rock beneath. In some sense, this phenomenon is similar to my Ice-fall hypothesis along the edges of the Southern branch of the Jakobshavn Isbræ in West Greenland.

It is however still an open question, whether the series of crevasses, we see, is an annual or some kind of tidal signal…
Title: Re: PIG has calved
Post by: nukefix on November 18, 2015, 05:10:27 PM
Here's a low-resolution demonstration how CryoSat swath-processing improves results over traditional InSAR POCA.

Source: http://www.geos.ed.ac.uk/glaciology/cryotop (http://www.geos.ed.ac.uk/glaciology/cryotop)
Title: Re: PIG has calved
Post by: AbruptSLR on November 18, 2015, 06:40:13 PM
Glaciers exhibit many types of periodic surface features in addition to crevasses. The first image below shows a different periodic pattern well to the north of the area we're considering (yellow arrows). Note too the peculiar streaks visible only in Landsat (orange arrows) appear to originate solely at lineations, then extend down-flow, seeming to cast shadows.

It is premature to hypothesize about what wipneus is seeing in #402 and #412 because we are still in the early stages of constructing our GIS stack and collecting basic information. These features may curious but they're important only as observational proxies --  it's coastal region developments that drive significant change at Pine Island (as AbruptSLR notes in posts above).

While noting that others in this forum are far better qualified than I am to engage in satellite data analysis of glaciers; and that glaciers exhibit numerous types of periodic surface features in addition to crevasses; and that it is premature to hypothesize with confidence what Wipneus is pointing out in #402 and #412; nevertheless, I provide the following comments:

1. The yellow arrows on the second image in #422 are in the eastern portion of the image (not the north).
2. In the first image in #421 shows 2014 Cryosat 2 observations in the area Wipneus is looking at; which shows elevation loss as compared to earlier observations.  Thus, who knows how much ice movement is required cause bergschrund behavior in brittle ice.
3. Snow can infill areas subject to ice movement making instrumentation observations tricky to interpret.
Title: Re: PIG has calved
Post by: A-Team on November 18, 2015, 08:37:05 PM
I saw a quote the other day for 0.4 m WorldView imagery at ~$17 per km2, which adds up for Antarctica. Google Earth has Petermann covered with it though. I may just email the 2014 Icebridge pilot who flew that PIIS grid instead.

Edit: added the image of Mer du Glace, Chamonix France. The periodicity presumably arises from an annual snow/melt cycle (see next post). These are not crevasses (based on the many images of this same scene at google search) though you can see a couple of ice falls (frozen rapids) in the image.
Title: Re: PIG has calved
Post by: P-maker on November 18, 2015, 09:46:48 PM
After some thoughts – and a few back-of-the-envelope calculations - I have come to the conclusion, that these linear features must be annual.

A-team has provided excellent graphics from which we can count about 4.5 of these features per km (201/44 km).

At the 15 m resolution picture above (see #422), it is quite obvious that the dark snow-filled crevasses are about two pixels wide (  ̴ 30 m which is also often the case with bergschrunds in the Alps). The darkest streaks are most likely representing the finest snow in the deepest part of the crevasse, where the wind-deposited snow is compacting and sinking. Two white stripes on either side (appr. 1 pixel wide each) could be the rough edges of the crevasse, which are most likely characterized by erosional zastrugi features on the surface. Between the crevasses are wider grey areas – approximately some 7-10 times the width of the dark crevasse itself ( ̴ 200-300 m). All together this indicates an annual surface speed of between 250 and 350 m/y. As ASLR has already shown (#418), the surface speed is increasing from about 300 to 400m/y in this area  ̴ 164 km from the ice front (where the crevasse pattern begins) increasing to  ̴ 800 m/y some 120 km from the sea.

All those “thousands of associated streaks” mentioned by A-team (#422), are most likely depositional features – so called periodic snow drifts - associated with two-dimensional cavities in a flat plain (similar features described by Greeley & Iversen, 1985 fig. 6b p. 205).

Coming back to why we have not seen these features before, I reckon it’s a mixture of the new fine resolution in Landsat and Sentinel products and the fact that the surface of the PIG front has been lowered some 40-50 meters over the past decade or so. This lowering of the frontal parts could have contributed to stronger catabatic winds, which may have turned the area 120-164 km from the ice front into an erosional zone now, whereas in the old days, it was nearly always a purely depositional zone.

So, to sum up: The bergschrund crevasses may have formed at this topographic breakpoint each year for many decades, as the glacier speed-up happens here for topograhic reasons. In later years, these features may have been exposed due to glacier thinning at the snout, which could have led to stronger catabatic winds and snow erosion higher up on the glacier.

Title: Re: PIG has calved
Post by: nukefix on November 19, 2015, 08:44:39 AM
I'd say the streaks are sub-surface crevasses or cracks. They do not have to be wide to be visible on a radar image, just the presence of an ice-air interface is enough.
Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2015, 11:27:27 AM
In later years, these features may have been exposed due to glacier thinning at the snout, which could have led to stronger catabatic winds and snow erosion higher up on the glacier.

Katabatic wind patterns in Antarctica are more complex than just being related to the glacial surface elevation drop at the nose of the PIG/PIIS.  For instance, CryoSat has observed patterns (see first attached png) in the Antarctic snow pack/ice surface associated with the strong katabatic winds throughout Antarctica.  While the data discussed in the following extract and linked website do not extend to the coasts, these katabatic wind can/do cause scour of snow into the ocean which contribute both to changes in surface elevations and to SLR:

Extract: "Antarctica has some of the strongest and most persistent winds on Earth, which leave permanent erosional and depositional features on the surface and in the snow pack. The scientists found that that these wind-driven features modify CryoSat’s radar measurements in such a way as to produce the pattern that has been detected. "

http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/CryoSat_detects_hidden_Antarctic_pattern (http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/CryoSat_detects_hidden_Antarctic_pattern)

Furthermore, I note that unlike Greenland, the West Antarctic wind, snowfall, and PIG ice velocities are strongly correlated to the ENSO cycle, which can cause changes in the surface patterns that we can see in the surface of the PIG.

Edit: For reference, I provide the second attached perspective image showing an exaggerated vertical scale of the ice/snow surface elevations in the PIG/Thwaites area in 2009.
Title: Re: PIG has calved
Post by: A-Team on November 19, 2015, 04:23:47 PM
Mind telling us the vertical exaggeration (50x?), map projection (mercator?), original publication source, and location of raw data file for that 2009 hill-shaded surface DEM (which is also used unsourced over at the Hansen paper forum)?

I don't understand the purpose of the 'distance (km x 5)' for the two horizontal axes. That seems to say the full extent, 200 km, is only 40 km which would not bring the region under discussion in view (so why not just label 0,40?). Or does it mean a km is a km horizontally with 5x vertical exaggeration? There is almost always a separate z axis when this is intended.

Is it feasible to locate (overlay) the lineation area we are looking at, perhaps on a much larger format of the image?
Title: Re: PIG has calved
Post by: A-Team on November 19, 2015, 05:18:17 PM
linear features are annual. 4.5 lineations per km (201/44 km). dark snow-filled crevasses two pixels wide 30 m. darkest streaks finest snow deepest part, wind-deposited snow  compacting and sinking. Two white stripes on either side erosional zastrugi features on the surface. wider grey areas 7-10 times...indicates an annual surface speed of between 250 and 350 m/ 300 to 400m/y in this area  164 km from the ice front increasing to 800 m/y at 120 km/ “thousands of associated streaks”  are depositional features periodic snow drifts - associated with two-dimensional cavities in a flat plain (see Greeley & Iversen, Wind as a Geological Process 1985). not seen these features before new finder sensitivity in Landsat and better resolution Sentinel products   lowering of the frontal parts   stronger katabatic winds turned the area 120-164 km from the ice front into an erosional zone now, whereas in the old days  a purely depositional zone.
Wait a minute, crazy-making P-Maker! You have no business analyzing the imagery, making size measurements, citing a classical aolean depositional text -- and where you get off, offering predictions we could actually test using the satellite record? This is too much like science. We don't do data here. Go away, we're a brew pub on the fifth pitcher. All conjectures are equally valid. 2+2=5, claim whatever you want, no supporting docs necessary. [[irony alert]]

One more week of floundering around with this and we really must ask Mario Pelto for an explanation of what is going on here. He last posted a forum comment on Sept 6th. Pelto has written extensively about Pine Island glacier but, like everyone else, focused on the marine interface.

We have 868 registered members but only 3-4 who will look at the free Landsat images, ditto Sentinel, in free image software before freely posting at this free forum. It's not a time or cost issue then. Access? It doesn't seem to help to post and re-post the links to EarthExplorer and the Sentinel hub. Day job? There've been many studies of what web sites people actually visit at work.

Digging into the full satellite record is enough work that it is better spread across many people. But we're not doing that. Look however at latest Zachariae article and be amazed at what 6-7 people motivated about climate change can do.

On wikipedia, Antarctic sastrugi (too irregular for us) received an interesting comment:
White and black colors on sastrugi are not lights and shadows, they demonstrate difference in radioreflectivity of snow deposits on the windward and leeward sides of a sastruga.... At the windward end of a ridge, the base erodes faster than above, producing a recognizable shape of anvil tip pointing upwind. 
I tend to look mostly at present-day Landsat-8 and Sentinel-1A IW. The issue with earlier Landsats is not the ground resolution but sensitivity in the panchromatic channel. The big technological advance with 8 is the higher bit depth (4096 grays distinguished vs 256). What this means is nicely illustrated here: http://laurashoe.com/2011/08/09/8-versus-16-bit-what-does-it-really-mean/ (http://laurashoe.com/2011/08/09/8-versus-16-bit-what-does-it-really-mean/)

The 12-bit is hugely important for adjusting contrast with inevitably white-on-white cryosphere imagery. With Landsat-7 and earlier, some landscape details can not be brought out no matter how you tweak the sliders -- they were just not captured in the information-theoretic sense.

Anyone can improve on the initial Landsat contrast, but optimizing contrast adjustment for an entire individual scene (or selected parts of it), automating that, scaling up to a pre-compute (or an on-demand) for the entire Landsat-8 archive are beyond the scope of these forums.

I've worked out a scheme for soft-masking of adaptive contrast which has to be close to optimal. The upper reaches of Pine Island is a good instance of where an all-out enhancement effort is needed vs huge expense getting someone down there in a plane or huge risks of ground exploration.
Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2015, 05:20:06 PM
Mind telling us the vertical exaggeration (50x?), map projection (mercator?), original publication source, and location of raw data file for that 2009 hill-shaded surface DEM (which is also used unsourced over at the Hansen paper forum)?

I don't understand the purpose of the 'distance (km x 5)' for the two horizontal axes. That seems to say the full extent, 200 km, is only 40 km which would not bring the region under discussion in view (so why not just label 0,40?). Or does it mean a km is a km horizontally with 5x vertical exaggeration? There is almost always a separate z axis when this is intended.

Is it feasible to locate (overlay) the lineation area we are looking at, perhaps on a much larger format of the image?

Unfortunately, I originally posted the perspective view image on Feb 25, 2013, as Reply # 29 in the "Surge" thread, and I have since forgotten the source, but I believe it was from a PowerPoint presentation posted on the internet in 2012.
http://forum.arctic-sea-ice.net/index.php/topic,21.0.html (http://forum.arctic-sea-ice.net/index.php/topic,21.0.html)

As I am distracted at the moment, the best I can offer as more precise substitute is to look-up the findings of the austral summer of 2013-2014 iSTAR snow tractor traverse of the PIG as cited below & in the attached image:


http://blogs.egu.eu/divisions/cr/author/berger/ (http://blogs.egu.eu/divisions/cr/author/berger/)

Extract : "For iSTAR, a new approach was undertaken using two ‘tractor trains’. These consist of two Pisten Bully snow tractors towing two long poly sleds with fuel bladders and three metal cargo sledges including a living ‘caboose’; a converted shipping container with a cooking and living space (essentially a caravan fit for polar travel!). All this equipment was delivered by the RRS Ernest Shackleton to the Abbot Ice Shelf in February 2012 and driven to Pine Island Glacier ready for the first traverse the following season."

Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2015, 05:27:39 PM
As I believe that the Sentinel 1A images use radar they should not show snow induced sastrugi, but rather the crevasses beneath the snow.
Title: Re: PIG has calved
Post by: A-Team on November 19, 2015, 05:52:11 PM
look-up the findings of the austral summer of 2013-2014 iSTAR snow tractor traverse of the PIG as cited below & in the attached image: http://blogs.egu.eu/divisions/cr/author/berger/ (http://blogs.egu.eu/divisions/cr/author/berger/)

Extract : "For iSTAR, a new approach was undertaken using two ‘tractor trains’. These consist of two Pisten Bully snow tractors towing two long poly sleds with fuel bladders and three metal cargo sledges including a living ‘caboose’; a converted shipping container with a cooking and living space
Very helpful, I'd not heard of this. They surely studied the very features we've been looking at (though the original scientists crossing PIG "didn't know they were on a glacier"). Those would be istar09-08 relative to Wipneus' original imagery

These same tractors were used to pull the mega-ton NEEM dome over to NEGIS this spring. Must be quite noisy. I can see why they would bring two, probably a beer wagon since a plane rescue was not in the cards (unless they cleared an airstrip at one of the depoes).

We can, in theory, re-generate the perspective elevation map for our little region by cropping (95% savings) the latest big DEM at NSIDC and getting it out of whatever funky format it's stored in (another 95% savings!) into the plain 32-bit grayscale that should have been served via polygon select in the first place. Reverse image search was not able to relocate your ppt.

They were not exactly focused on surface features so let's hope there are lots of photos:

The iSTAR programme is split into four science projects with C and D being the overland traverse of Pine Island Glacier.

iSTAR C aims to understand the internal dynamic processes responsible for transmitting the effect of thinning of PIG’s floating ice shelf caused by melting of warm ocean currents upstream into the trunk and tributaries of the ice stream. Of particular interest is how the underlying geology of the ice influences its flow.

Over the course of two field seasons the traverse collected 2000 km of radar data by skidoo and 40 km of seismic surveys to get detailed images of the ice thickness and bed topography. Surface radars operated at the same frequency as the satellites to improve estimates of ice volume loss from West Antarctica.

iSTAR D looked at past snow accumulation and ice density to improve estimates of ice loss that cannot be determined from satellite measurements. To determine past accumulation and understand surface processes such as snow density changes and compaction, they drilled 10 shallow (50 metre) ice cores. These ice cores had to be kept frozen and shipped back to the UK where their chemistry is being analysed to enable us to quantify how much snow has fallen onto the ice sheet in the past. Over 20 snow density profiles were recorded using a neutron probe.

More at http://www.istar.ac.uk/ (http://www.istar.ac.uk/)
Title: Re: PIG has calved
Post by: Sleepy on November 19, 2015, 06:35:43 PM
Pardon, but I haven't read or followed this thread very much lately, but regarding the picture in #429, it can be found in this paper from 2002 by Bamber and Rignot.
http://escholarship.org/uc/item/1p17h4rz (http://escholarship.org/uc/item/1p17h4rz)

It refers to Bamber, J.L. and R.A. Bindschadler. 1997. An improved elevation dataset for climate and ice-sheet modelling: validation with satellite imagery. Annals of Glaciology 25:438-444.

https://nsidc.org/data/docs/daac/nsidc0076_antarctic_5km_dem.gd.html#bamber97 (https://nsidc.org/data/docs/daac/nsidc0076_antarctic_5km_dem.gd.html#bamber97)
Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2015, 06:48:47 PM
Pardon, but I haven't read or followed this thread very much lately, but regarding the picture in #429, it can be found in this paper from 2002 by Bamber and Rignot.
http://escholarship.org/uc/item/1p17h4rz (http://escholarship.org/uc/item/1p17h4rz)

It refers to Bamber, J.L. and R.A. Bindschadler. 1997. An improved elevation dataset for climate and ice-sheet modelling: validation with satellite imagery. Annals of Glaciology 25:438-444.

https://nsidc.org/data/docs/daac/nsidc0076_antarctic_5km_dem.gd.html#bamber97 (https://nsidc.org/data/docs/daac/nsidc0076_antarctic_5km_dem.gd.html#bamber97)

Sleepy,

Thanks for the great detective work, & it looks like I misinterpreted the information in the ppt that I found that image in, as clearly the elevations are from well before 2009 (which date I believe that I confused with being sourced from another 2009 Rignot paper on the PIG).

Best,
ASLR
Title: Re: PIG has calved
Post by: A-Team on November 19, 2015, 09:07:57 PM
Based on the iStar route through 60km of our "crevasse field" we can be certain that it is anything but. Nobody is going to drag a 168,000 lb fuel bladder over a snow bridge much less down into a crevasse. Nobody in their right mind would even take a chance on that at such a remote location.

With that Pisten Bully traverse of Greenland, a specialized team scouted a route for the first 100 km using a radar boom that stuck out 10 m ahead (when they weren't using a similarly equipped robotic vehicle). The radar signature is shown in the 2nd image.
Title: Re: PIG has calved
Post by: A-Team on November 19, 2015, 09:17:56 PM
Nice work by Sleepy! That 1997 DEM is not of use to us -- the km x 5 turns out to mean the pixel size is a mere 5 km, everything else is interpolated. However part a) of that figure, which shows that the region of interest is almost entirely between 0 and 1% slope, rules out bergschrunds. These form at the very steepest parts of a glacier if at all.

No bergs, no bergschrunds. No ticket, no laundry. Here we know from the satellite radar grid  -- 4th image in #416 -- that this area of Antarctica is like Greenland: ice all the way down to sea level and below. Indeed this retrograde slope behind the calving front is the whole reason Pine Island is in the news.

NSIDC will host a hugely improved DEM file today. Also I recall Howat was producing very high resolution DEMs from WorldView stereo.

So we are left with some sort of annual wind accumulation feature as proposed by P-Maker or frozen compression or extension wave. It is easy enough to compare 2014 with 2015 to see what if anything is new with the transverse arcs and their attached streaks. 2015 should have a single new one at the highest position under this theory (but if I recall, it doesn't).
Title: Re: PIG has calved
Post by: P-maker on November 19, 2015, 10:03:34 PM
A-Team

yes, who would cross a crevasse with 84 t of fuel on a steel plate?

In fact, they did not cross the bergschrund zone!

At istar07 (some 180 km from the glacier front – see image in #432), they made a sharp right turn.

Access to log books could help clarify why they made this turn. Could it be that their scouts on skidoos ran into the crevasse zone ahead of the convoy?

As another matter of fact, I believe these caterpillars “tread more lightly”, than you and I.

I am furthermore convinced that these 30 m wide crevasses are filled with fine-grained, frozen snow, so they are easily crossed most of the time.
Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2015, 10:34:06 PM
I'd say the streaks are sub-surface crevasses or cracks. They do not have to be wide to be visible on a radar image, just the presence of an ice-air interface is enough.

It would be good if someone more skillful than me were to compare nukefix's Sentinel-1 dual-pol image from #175 (see first attached image), #178 & #180 for August 23, 2014, with Wipneus' Nov 11, 2015 Sentinel-1 image to see what patterns have changed.

Furthermore, I note that the PIIS is so large that as it floats up and down the glacier is deformed tens of kilometers upstream from the grounding line (see the second image of an ESA simulation)

Next, again I note that the ice flow velocity of the PIG changes with the ENSO cycle (slow during a La Nina and fast in an El Nino) and that per the third attached image 2011 was a La Nina year (and such oscillations in ice velocity could cause banding of the crevasse patterns).

Lastly, further to both P-maker's and nukefix's points any crevasses would likely be infilled with snow as indicated by the attached 2009 fourth image from the PIG taken from the following website with the caption below.

http://blogs.ei.columbia.edu/2009/10/28/over-pine-island-glacier-west-antarctica/ (http://blogs.ei.columbia.edu/2009/10/28/over-pine-island-glacier-west-antarctica/)
Caption for fourth image: "Snow-covered crevasses near the edge of Pine Island Glacier. Small meltwater ponds are visible even though it's early in the Antarctic summer."


Edit: nukefix notes that the width of the upstream crevasses could be relatively thin and could still be seen by Sentinel-1's radar.
Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2015, 10:44:47 PM
Just to give people a better idea of how far the PIG ground line is from the calving face I provide the attached January 30, 2012 Terra image
Title: Re: PIG has calved
Post by: AbruptSLR on November 19, 2015, 11:28:44 PM
As noted in the linked article between March 3 and 15, 2015 the PIG ice fast surged by about 100meters (see attached Sentinel-1 image):

http://www.livescience.com/50254-fast-flow-pine-island-glacier.html (http://www.livescience.com/50254-fast-flow-pine-island-glacier.html)


Extract: "One of West Antarctica's largest glaciers surged a staggering 325 feet (about 100 meters) in less than two weeks this month, the European Space Agency reports.

Two radar images from the ESA's Sentinel-1A satellite on March 3 and March 15 reveal parts of the enormous Pine Island Glacier and its floating ice shelf making a swift trek toward the sea."
Title: Re: PIG has calved
Post by: oren on November 20, 2015, 09:15:23 AM
As noted in the linked article between March 3 and 15, 2015 the PIG ice fast surged by about 100meters (see attached Sentinel-1 image):

http://www.livescience.com/50254-fast-flow-pine-island-glacier.html (http://www.livescience.com/50254-fast-flow-pine-island-glacier.html)


Extract: "One of West Antarctica's largest glaciers surged a staggering 325 feet (about 100 meters) in less than two weeks this month, the European Space Agency reports.

Two radar images from the ESA's Sentinel-1A satellite on March 3 and March 15 reveal parts of the enormous Pine Island Glacier and its floating ice shelf making a swift trek toward the sea."

The image is impressive (and the "crevasses" or whatever they are can be seen) but the surge is not. As PIG moves about 4 km/y, or about 10 m/d, 100 meters in 12 days is just about average.
Title: Re: PIG has calved
Post by: AbruptSLR on November 20, 2015, 11:03:59 AM
In the way of identifying more sources of potential deformations of the PIG that might be sufficient to fracture the ice [besides: (a) tidal/storm surge induced flexing of the PIIS deforming the ice upstream of the grounding line, and (b) periodic changes in the ice flow velocity associated with the ENSO cycle], I note that: (1) the periodic major calving events for the PIIS must cause an abrupt upstream response, and (2) changes in the bottom topography elevation must cause stresses in the ice field to accommodate geometry.  As I do not have access to the BEDMAP2 data of bottom topographies, regarding the second point: attached is a re-posted figure (from my Reply #6 of the "Surge"thread) from Gladstone et. al 2012 of the output from a box model of sub ice shelf advective circulation of CDW into (and out of) the PIG subglacial cavity for SRES A1B until 2100, and where the light brown shaded area in the top panel shows the bottom topography.  Note that the blue histogram indicates the likehood (per their model) that the groundling line will reteat to the indicated rectangle by 2100, while the green histogram indicates that the groundling line retreat might temporarily stall in area indicated by the associated rectangles.

I am not saying how impressive any of these deformations are, or are not, but they all should be considered when evaluating the patterns shown in the Sentinel-1 images.
Title: Re: PIG has calved
Post by: A-Team on November 20, 2015, 12:45:44 PM
good to compare nukefix's Sentinel-1 dual-pol image from #175 (see first attached image), #178 & #180 for August 23, 2014, with Wipneus' Nov 11, 2015 Sentinel-1 image to see what patterns have changed.
We are better off with Landsat because of the slow motion here (as translated to pixel displacement vs alignment error) and many years of coverage. Sentinel is unable to pick up the streaks whose ironclad association with the lineations is critical to any proffered interpretation. (The first image below, taken from #180, shows the 'crevasses' crossing all over each other and may faintly show streaks in the upper part.)

Note the nukefix images from austral winter of 2014 (#175 #178 #180 all on page 4) are flipped horizontally relative to wipneus' Nov 11, 2015 Sentinel. The correct orientation seems the latter going by ESA #442. Sentinel follows some poorly thought-out practice of encoding a petty scene detail with choice of mis-orientation. (Petermann images are often completely katywumpus too.) Dear ESA: put yr metadata in the metadata file and clean up the ridiculous file names.

The Antarctic settled long ago on polar stereographic coordinates, Greenland on UTM mercator. Since the Toolbox wasn't operational at the time nukefix made those images, they'd still be in native Sentinel. However from the Landsat 2015 animation in #413, we know 6 months is already sufficient at 15 m to see warpage of the lineations.

Wipneus posted at 50 m and 10 m; those resolutions would have to be matched. nukefix wrote back then of the
'arcuate crevasses on the trunk on 23 Aug 2014 ... the scale of this thing is mind-boggling - the width of the [#175] scene is 70km'. The posted image was 1312 pixels wide, that works out to 53 pixels per meter which very likely means 50 m.

The scale in the overview #178 is closer to 100 m; this needs a horizontal flip and 90º CCW rotation to match wipneus. In the 'full-resolution zoom' of #180, the scale is surely Sentinel default. The region provided with the full zoom is not identified relative to #175 but that is resolved in the 2nd image below.

The accession number, presumably s1a-iw-grd-hh-20140823..., was not provided either (for those wishing full zoom over the whole region) but that's quickly found from location and date provided if only the Sentinel hub weren't broken down again.

Stop apologizing, discard the unfixable code and start over, even if it means moving the server out of your Mom's basement (3rd image):

"19 Nov 2015 High Workload on SciHub: maintenance activity ongoing. Dear users, in the last two days the Scientifc Data Hub has been subject to high workloads. These have brought to a temporary degradation of the service performances. Maintenance activities are currently on-going for resolving the issue. We apologise for any inconvenience caused."

No bergs, no bergschrunds. No ticket, no laundry. The whole point of Pine Island is the retrograde bed. See any of the radar tracks in #416: nothing to see here by way of bedrock topography, please move along.

Some arrows showing the snow covered crevasses near the coast in 4th image of #440? I am only seeing yardangs and indurated surface, the caption notwithstanding.

Finally, returning to Abrupt's request for a Sentinel animation of nukefix #175 and wipneus #402 which are 454 days apart, the scales, and projections do seem to match up. The hh of #175 is likely the R of an RGB decomposition though gimp 'desaturate' provided better balance. Both grayscales needed adaptive contrast adjustment done in ImageJ.

The question here is ground control points, rather lack thereof. Wipneus' image is displaced a dozen pixels or so vertically from nukefix's in the 'hairdresser' region. Does this represent motion, different cropping, different Sentinel processing? nukefix ended up at 1312x880 whereas wipneus posted at 1240x816, numbers inconsistent with uniform rescaling (1.058 vs 1.078 h vs v).

The full resolution animation below, which needs a click, awaits clarification. It would be better to start over and run both through the Toolbox to get them both in polar stereographic at the same scale and processing history, along with some lat,lon geocoding for fixed points. Or dates with appropriate seasonal matching. Meanwhile I have a better quartet of Landsats that does all this and more....
Title: Re: PIG has calved
Post by: nukefix on November 20, 2015, 02:47:12 PM
Once scihub is up I can reprocess (they seem to be busy preparing for opening the S-2 archive for the world at the moment). What is the approximate speed per day in this region? I could do RGB in Polar Stereographic with sufficient interval to see the changes.

ps. there's nothing that weird in Sentinel-products, ground-range detected is a rather standard way of delivering imagery due to historical reasons and metadata is in the products themselves as it should be. Just use correct tools (not tools made for photo-graphy) to pre-process the imagery and you'll be fine! Also for S-2 the choice of jpeg2000 was dictated by the need to have a 'streaming' format that could handle multi-resolution bands and not incompetence/malice of European satellite industry.

pps. Bergschrund is not the correct term to use here as it refers to the crevasse that opens up at the point where the glacier becomes so thick that it starts flowing (few tens of meters).

ppps. I'm betting that the cracks are caused by curvature of the glacier-bed, a quality DEM or altimeter-track could show what the surface of the glacier is doing in the z-direction..
Title: Re: PIG has calved
Post by: P-maker on November 20, 2015, 03:52:29 PM
Nukefix,

pps. Bergschrund is not the correct term to use here as it refers to the crevasse that opens up at the point where the glacier becomes so thick that it starts flowing (few tens of meters).

I believe you are correct. The term should be transverse crevasses (c.f. #406).

The surface moves about 1 m per day, possibly a bit more, when the cracks open.
Title: Re: PIG has calved
Post by: A-Team on November 20, 2015, 04:26:02 PM
Aha, we're making progress if the surface is concave upwards. Note the arches switch their curvature from positive to negative, passing through a zone where they are straight.

Following up a bit on the image Abrupt posted in #442. It appears to be a March 2015 interferogram by new PhD Anna Hogg, perhaps done for a meeting talk or paper in press. I don't understand what the IV (m) means on the key, maybe 'interferometric velocity in meter per day'. It seems from their twitter chatter that they converted fringes into distance moved over the 12 days.

Something here does not quite make sense as the very fastest zones are shown next to the very slowest, that shear would isolate a visible ice stream. We do see a lagging zone in the arches but over on the other side.

The animation below shows why you always want to take the tif version rather than the lossy jpg. it should animate without a click (and is now, seems to need vertical cut to 699 or fewer pixels).

https://twitter.com/hashtag/esafringe?src=hash
https://twitter.com/CPOM_news
Title: Re: PIG has calved
Post by: AbruptSLR on November 20, 2015, 05:27:22 PM
The whole point of Pine Island is the retrograde bed.

Thanks for the great images, animations, and analysis; and as I do not have mad image processing skills I will continue writing about back story issues and implications for future model projections for the PIG.

Certainly, the most prominent mechanism for the PIG's recent behavior has been the retrograde bed & the oceanic induced melting at the grounding line.  However, as indicated by the Gladestone et al. 2012 analysis/image, and the ESA SAR Interferometry image in #440, by the 2011-2012 season the grounding line reached the bottom of the retrograde slope and furthermore, per Dutrieux et al. (2014), during the 2010-2011 La Nina the grounding line melting for the PIG decreased by about 50% (between January 2010 and 2012):

Dutrieux P, Rydt JD, Jenkins A, Holland PR, Ha HK, Lee SH, Steig EJ, Ding Q, Abrahamsen EP, Schroder M (2014), "Strong sensitivity of Pine Island ice-shelf melting to climatic variability", Science, 343 (6167), 174-178, DOI: 10.1126/science.1244341

http://www.sciencemag.org/content/343/6167/174 (http://www.sciencemag.org/content/343/6167/174)

Extract: "Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event."

See also:
Steig EJ, Ding Q, Battisti DS, Jenkins A: Tropical forcing of circumpolar deep water inflow and outlet glacier thinning in the Amundsen Sea Embayment, West Antarctica. Annals of Glaciology, 53, 19-28 (2012).
http://www.atmos.washington.edu/~qinghua/pdf/19.pdf (http://www.atmos.washington.edu/~qinghua/pdf/19.pdf)

Ding Q, Steig EJ, Battisti DS, Wallace JM: Influence of the tropics on the Southern Annular Mode. Journal of Climate, 25, 6330-63 (2012).
http://www.atmos.washington.edu/~qinghua/pdf/21.pdf (http://www.atmos.washington.edu/~qinghua/pdf/21.pdf)

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83

The impact of the combination of the grounding line reaching the bottom of the retrograde and the 2010-2011 La Nina on the PIG ice flux can clearly be seen in the attached image from the
2014 Rignot paper at the following link (reposted):

http://www.ess.uci.edu/researchgrp/erignot/files/grl51433.pdf (http://www.ess.uci.edu/researchgrp/erignot/files/grl51433.pdf)

Thus, the implications of the Anna Hogg image/analysis from March 2015 is that from suppressed ice flux conditions from 2010 to 2014 the failed El Nino of the 2014-2015 season restored the ice velocities back to the pre-2010 levels (4km/yr).  Thus the bottom topography of the PIG is only part of the story and ENSO cycles and more importantly future atmospheric warming following a BAU pathway to about 2038 per DeConto and Pollard (2015)  will likely drive cliff failures and hydrofracturing that will accelerate ice mass loss from the PIG significantly as the image analyses in this thread show that there are plenty of preformed crevasses in the PIG/PIIS to promote future cliff failures driving by hydrofracturing.

With a hat-tip to Lennart van der Linde for the DeConto and Pollard reference below:

"DeConto and Pollard are expected to publish a new paper on Antarctica in the coming months. So let's see what they have to say in addition to this sneak preview of their findings:
http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf (http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf)

"the magnitude and rate of Antarctic ice sheet retreat are highly dependent on which future greenhouse gas scenario is followed, but even the lower emission scenarios produce an Antarctic contribution of several meters within the next several centuries. Once atmospheric CO2 concentrations exceed 2x preindustrial levels, we find that hydrofracturing by surface melt on ice shelves can trigger large-scale ice sheet retreat, regardless of circum-Antarctic ocean warming. Hence, unlike the LIG, atmospheric (not ocean) warming has the potential to become the primary mechanism driving future retreat of the Antarctic ice sheet. In simulations without atmospheric warming, we find small amounts of ocean warming can still produce large-scale retreat of the West
Antarctic Ice Sheet, although the timescale of ocean-driven retreat is slower than atmospherically driven retreat.""
Title: Re: PIG has calved
Post by: AbruptSLR on November 21, 2015, 05:27:19 PM
Aha, we're making progress if the surface is concave upwards. Note the arches switch their curvature from positive to negative, passing through a zone where they are straight.

...

Something here does not quite make sense as the very fastest zones are shown next to the very slowest, that shear would isolate a visible ice stream. We do see a lagging zone in the arches but over on the other side.

While I am sure that we are in for even better visual treats from A-Team, nukefix, Wipneus and many others, A-Team's initial animations make several point relatively clear including:

(1) To state a few obvious points: (a) the direction of ice flow downstream due to gravity is roughly normal to the face of the transverse crevasses [where the principal tensile stresses cause the transverse crevasses]; and (b) the inflow of lateral ice streams, marginal shear, and bends in the flow directions all modify the stress fields in the main ice stream as it moves downstream, first through an area with a very flat surface slope and then into a zone with a steeper slope [see the image in #438] as the ice accelerates and thins.

(2) The ice "arches" between the transverse crevasses switch curvature from positive to negative [passing thru a zone where they are straight, as A-Team notes] because inflow of lateral ice from the North and South initially support the positive arch shape, but as the ice stream velocities near the middle of the field accelerate [relative to the margins], the arches first flatten and then develop a negative curvature. There could be a minor amount of compressive creep, and plastic deformation, in the ice within the arches; however, I suspect that the different speeds of the ice flow between the margins and the middle of the field is the main reason for the indicated behavior.

(3) The lagging zone to the South side of the arches (noted by A-Team) is most likely due to the fact that the catch basin to the South is much larger than to the North, and thus the larger inflow of ice flux slows the downstream ice velocities to the South in this area.

(4) Between nukefix's image & Wipneus' image we see new transverse crevasses forming upstream of the old crevasse (even while the old crevasses are slowly moving downstream) as the flow area is enlarging.  Furthermore, due to the relatively slow ice velocities upstream (compared to downstream) the width of the transverse crevasses remain narrow, because the flat sloped area (see image in #438) prevents the downstream ice arches from accelerating away from the upstream arches.

(5) The animation(s) also show marginal shear crevasses forming on the margins and at bends in the ice streams.
Title: Re: PIG has calved
Post by: AbruptSLR on November 21, 2015, 05:40:19 PM
To elaborate on some of my comments about the influence of the influx of lateral ice streams for the PIG; I provide the following linked reference and associated images discussing impacts on ice flow patterns and of compressive creep with time (note that the length of the arches cited by A-Team are longer in the zone of positive curvature and shortest when flat, so that as the arches are too thick and well confined to buckle, the length of the arches reduce by a combination of creep and vertical convection through the thickness of the ice streams (see the first image).  Also, I note that as Hughes (2012) focuses on the Byrd Glacier, that his notes about a subglacial lake are not relevant, but I do note that the vertical convective motion causes internal friction that causes ice melt to rain down through the PIG to contribute to basal melt water that flows down the bed stream and out into Pine Island Bay, thus lubricating flow and contributing to future accelerations of the ice flux.

Terence J. Hughes, (2012), " Thermal convection in ice sheets: New data, new tests", Natural Science, Vol.4 No.7, Article ID:20743,10 pages DOI:10.4236/ns.2012.47056

http://file.scirp.org/Html/1-8301678_20743.htm (http://file.scirp.org/Html/1-8301678_20743.htm)
Title: Re: PIG has calved
Post by: AbruptSLR on November 21, 2015, 08:09:59 PM
As this thread is named "PIG has Calved", I offer the following discuss about recent and future calving from the PIIS:

(1) I have expressed my opinion (which some argue with) in Replies # 218, 220, 225, 261 and 336 that recent and near-term (2016 to 2040) major calving for the PIIS is/will-be dominated by splitting tension stresses associated with compressive fields induced by lateral ice inflow from the Southwest, SW, Tributary Glacier forming a major rift in the ice shelf.  As a side-note I speculate that the next major rift will form a failure mechanism by about July 2016 with a major calving following sometime between July 2016 and November 2016, depending on boundary conditions and on whether fast sea ice is present.

(2) In Reply #449 I expressed my opinion that the current Super El Nino is promoting the advection of larger than typical volumes of warm Circumpolar Deep Water, CDW, beneath the PIIS; which in my opinion is currently causing the grounding line to retreat upstream relatively rapidly across a relatively flat portion of the PIG's bed.  Here I note that I expect a positive PDO to result in a period from 2015 to about 2035 with an above average number/strength of El Ninos that will keep the grounding line retreating upstream across this approximately 40 to 50km long flat portion of bed, where I expect the grounding line to become temporarily pinned by 2040 by the bottom ridge at the "stable position" indicated in the first image from Gladestone et al (2012).

(3) As the grounding line retreats upstream through about 2035-2040 I expect both basal melting (with irregular bottom grooves) and accelerations of local ice velocities to further thin the PIIS so that by 2035 to 2040 I expect the calving face to migrate upstream from the SW Tributary interface due to melt pond failures (see Reply #382, and DeConto, Pollard and Alley's hydrofacturing work).

(4) From 2040 to about 2060, I expect the PIIS calving face to progressively move upstream to the "stable position" shown in the first image.  Furthermore, I expect this calving behavior to be controlled by mechanisms discussed by Jeremy Bassis, of the University of Michigan, in the linked WAIS Workshop PPT and the second, third and fourth attached images; together with accelerating input from melt pond failures of the pre-formed transverse crevasses near the PIIS calving face as I expect the atmospheric CO2eq concentration to reach twice the pre-industrial levels in the 2038 to 2045 timeframe.

https://www.waisworkshop.org/sites/waisworkshop.org/files/files/agendas/2013/presentations/session6/Bassis.pdf (https://www.waisworkshop.org/sites/waisworkshop.org/files/files/agendas/2013/presentations/session6/Bassis.pdf)

See also:
http://www.nature.com/ngeo/journal/v6/n10/full/ngeo1887.html (http://www.nature.com/ngeo/journal/v6/n10/full/ngeo1887.html)
&
Heeszel, D. S., H. A. Fricker, J. N. Bassis, S. O'Neel, and F. Walter (2014), Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure, J. Geophys. Res. Earth Surf., 119, 731–744, doi:10.1002/2013JF002849.

http://onlinelibrary.wiley.com/doi/10.1002/2013JF002849/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013JF002849/abstract)

(6) By 2060 I expect the PIIS to have disappeared and I expect that cliff failures and hydrofracting could thereafter (to at least 2100) cause the calving face to retreat relatively rapidly upstream depending on whether atmospheric conditions sustain periodic surface ice melting during the austral summers near the PIG calving face.
Title: Re: PIG has calved
Post by: AbruptSLR on November 23, 2015, 10:52:25 AM
The attached image from Mouginot et al. (2014) makes it clear that during the faux hiatus period (including the strong 2010/11 La Nina) the ice velocities of the PIIS slowed, on average, while the upstream areas of the PIG accelerated. This indicates that ice flux from the PIG is far from equilibrium; particularly as the current Super El Nino is likely currently accelerating the advection of warm CDW to the PIG grounding line and basal areas of the PIIS.

Caption: "Pine Island Glacier has a 30-kilometer-wide grounding line fed by nine glaciers. Thwaites Glacier has a 120-kilometer-long grounding line. To the west, a 60-kilometer-wide fast-moving portion of the Thwaites Glacier forms an ice tongue. To the east, a slower-moving portion of the glacier flows into an ice shelf buttressed by ice rumples. Bedrock mapping suggests that this buttressing wall is more easily breached than previously thought. These maps show flow-speed changes in Pine Island (a) and Thwaites (b) Glaciers. Red indicates greater increases in flow speed. The green lines indicate the position of the flow-speed contours four the years 2006-2013. Image courtesy (Mouginot et al. 2014)"

Mouginot, J., E. Rignot, and B. Scheuchl. 2014. Sustained increase in ice discharge from the Amundsen Sea Embayment, West Antarctica, from 1973 to 2013. Geophysical Research Letters 41: 1576-1584, DOI: 10.1002/2013GL059069

http://onlinelibrary.wiley.com/doi/10.1002/2013GL059069/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013GL059069/abstract)

Abstract: "We combine measurements of ice velocity from Landsat feature tracking and satellite radar interferometry, and ice thickness from existing compilations to document 41 years of mass flux from the Amundsen Sea Embayment (ASE) of West Antarctica. The total ice discharge has increased by 77% since 1973. Half of the increase occurred between 2003 and 2009. Grounding-line ice speeds of Pine Island Glacier stabilized between 2009 and 2013, following a decade of rapid acceleration, but that acceleration reached far inland and occurred at a rate faster than predicted by advective processes. Flow speeds across Thwaites Glacier increased rapidly after 2006, following a decade of near-stability, leading to a 33% increase in flux between 2006 and 2013. Haynes, Smith, Pope, and Kohler Glaciers all accelerated during the entire study period. The sustained increase in ice discharge is a possible indicator of the development of a marine ice sheet instability in this part of Antarctica."
Title: Re: PIG has calved
Post by: A-Team on November 23, 2015, 01:07:58 PM
Some excellent analysis in the last posts, indeed we are looking at surface expression of the evolving upper trunk stress field.

The lower end can do whatever it wants but nothing happens to sea level from melting of a floating shelf or from grounding zone retreat per se. Models don't raise sea level. The trunk has to get in motion; otherwise the ice volume is just not there.

While we await the arrival of the future at Pine Island, the situation may be more simply and sensitively monitored by trending motion of trunk surface features: the opera hasn't started until the large lady sings.

A few more thoughts on our off-thread excursion: animations are not merely pleasing visuals but rather a study of the  time evolution of a dynamic system. The satellite record is precious so we seek to exhaust it informatically. Having expanded the past to the present in a power series, the near future will follow the fit.

Because this has to be done for every glacier in the cryosphere, we are looking for a large scale automated pre-compute. If a point-and-click algorithm exists (eg animated velocity interferograms for rolling pairs of Sentinel 1A's), then running it does not constitute original research and scientists doing so need redeployment. Factorization is a huge force-multiplier.

Pine Island's trunk seemed like a very favorable prototyping situation because it's so evenly gridded with surface markers. However I encountered a large number of pesky issues in making multi-year Landsat animations.

I'll skip over the ones where it says north is up when south pole is obviously up, where the central meridian (in Antarctica's polar stereographic coordinates PS) is provided in the scene portal but dropped out of the download, and where scenes of the same path,row come in software-disrupting petty dimensional variations such as:

path,row 229,114   path,row 232,113
17541 × 17641       17161 × 17241
17561 × 17601       17161 × 17261
17561 × 17621       17181 × 17261

Inland Antarctica is quite cloudy. Landsat-associated cloud metadata don't speak specifically to a region of interest (which is not fully known at the outset). EarthExplorer provides a very peculiar quality file (eg LC82291142015320LGN00_QB) that could serve as a cloud cover mask. It's not in the download packet though. The idea here is to intersect masks (ROI with QB blue) at the time of search to trigger a bulk download of the useful files instead of walking manually through terabytes of clouds.

I've got a question in to their help desk about how these are supposed to be co-registered (and why the heck doesn't USGS offer this in the first place). They will probably just pass me off on gdal but the problem is that the trunk of Pine Island doesn't have good ground control points -- everything is moving or if fixed, covered with drifting snow. How would I know that gdal is working?

The top of images get squeezed in PS and so the slightest error in registration becomes fully comparable to the actual motion between scenes. If a rotation is needed to bring everything to a common meridian, say 096ºW, that rotation would have to be about the south pole, which is some 1600 km beyond scene boundaries. Gimp is capable of an out-of-scene center of rotation but this might be a bit much.

Factorization ... the idea has not penetrated very far into geo.

In the first image, I sought to fix the A Hogg velocity map so that it might be compared to the clean offering of the Rignot group. However the color key was chosen poorly and this potentially simple task (10 seconds of gimp layer math) becomes unfeasible. Software with giant pull-down menus of pseudo-scientific color keys has been a huge source of problems in glaciology.

The next two images show, in Sentinel and Landsat respectively, crisscrossing of lineation fields in different years and regions. So the first round evidently has been over-written by later developments. I don't have the earliest pattern establishment dated. The Landsat also shows the interplay between the eolian snow drifts (?) and the lineations.

I'll post more of a time series after getting the registration issues resolved. These Landsats are fairly clear and span 715 days, much longer than we have from Sentinel. Some of the snow drifts are persistent but others come and go.

Looking into the 'display issue' vs the vast scale of Antarctica, a 27" retinal display iMac ($1650 new, box opened) can show an animation 28 times the maximal size allowed at this forum but even that -- 71 km by 40 km or 2840 km2 at 15 m Landsat resolution -- is not quite enough for full width of the PI trunk and close-in arms of tributaries.

 2013 312 231 114  LC82311142013312LGN00_B8.TIF
 2013 335 232 113  LC82321132013335LGN00_B8.TIF
 2013 344 231 113  LC82311132013344LGN00_B8.TIF

 2014 013 229 114  LC82291142014013LGN00_B8.TIF
 2014 258 232 113  LC82321132014258LGN00_B8.TIF
 2014 349 229 114  LC82291142014349LGN00_B8.TIF
 2015 064 229 114  LC82291142015064LGN00_B8.TIF

 2015 261 232 113  LC82321132015261LGN00_B8.TIF
 2015 293 232 113  LC82321132015293LGN00_B8.TIF
 2015 304 229 114  LC82291142015304LGN00_B8.TIF
 2015 320 229 114  LC82291142015320LGN00_B8.TIF
Title: Re: PIG has calved
Post by: nukefix on November 24, 2015, 10:47:25 AM
Does anyone have a ballpark estimate on the speed of the movements of the lineations? I need some estimate in order to pick a nice triplet...
Title: Re: PIG has calved
Post by: A-Team on November 24, 2015, 02:26:53 PM
Nicely spaced triple would be great.

I've noticed that ESA and others keep putting out these 12-day repeat images that simply don't work because there has not been enough movement except at the snouts of the very fastest glaciers. One size doesn't fit all -- probably have to montage the outcomes from repeat intervals optimized to different velocities.

It is really quite hard to read off velocities on these illustrations because of  (1) sparsely labelled logarithmic color keys which (2) weren't embedded in the map and so didn't undergo the same color transformation causing the correlation between key and map colors to be lost plus (3) the velocity layer was collapsed onto an underlying satellite grayscale whereas the key was not, followed by separate jpg compressions of key and map.

Unlike in Cartography 101, if you click on a particular color in the key with a tool that can find that same color everywhere else on the map, it won't work regardless of how you set the color radius. The 1st image in #422 shows the velocity contours (isotachs) but their labels or spacing is not known (other than it is logarithmic).

#414-#422 have our best estimates of velocities (and also rates of vertical thinning). In the central region of the trunk, just up from the funnel throat, #418 for 2011 1-2 km per year (5 m per day) in the fastest region but fallowing off to 1 m per day on the side of an (arched) transect orthogonal to flow lines.

So at 15 m resolution @ 12 days, that would 1-4 pixels of movement, probably not enough relative to other issues.

The first image below shows the H grayscale of a HSV decomposition of the log velocity RGB provided by Mouginot (repeats 2nd image in #416)

The second image shows the log isotachs (32 grades) as contoured online at G'MIC with 0.3 degrees of smoothing. The third exponentiates the original H over at ImageJ and contours as above followed by histogram normalization.

This seems to work ok -- the scale ranges from 0 to 3 km per year so the isotachs are separated by 34 m per year -- but you can see the curvy mess this creates in the color key which is supposed to be clean vertical bars of width 8.

Our region of interest is slightly above the first tributary trunk coming in from the right, as illustrated by the dotted in the 4th image. This whole process of making the 4 images took me OVER 10 MINUTES (grr!?$#@!) so we cannot expect busy glaciologists to produce reader-usable products for journal articles, regardless of unlimited space available in article supplemental.
Title: Re: PIG has calved
Post by: A-Team on November 24, 2015, 03:05:45 PM
Here are the 5 cloud-free Landsats of path,row 229,114. They are not really aligned as I'm still awaiting word from Landsat (after holidays, or will they forget altogether?) as to what they did vis-a-vis polar stereographic. To get movement accurately especially with mixed path,rows  to remove projection error.

However the images, 15 m resolution of the upper right corner of the box in the previous post, do give some idea of the stability of the lineations and streaks (not so much). I'll add the other 6 dates in a bit (these require individualized contrast reprocessing) to give a 715 day span of monitoring and see if there is not a common fixed ground control point.

Note blog width of 700 pixels only covers 10.5 km at Landsat 15 m resolution whereas the feature here is ~70 km wide and perhaps 40 km in height so there has to be some selection on what sub-scenes are of interest, or else stand back and look at lesser resolution.

The time interval between cloud-free Landsats is very erratic and no images can be taken during the dark months which together would make for rather jerky animations. Thus Sentinel has some real advantages (though it does not do as well at imaging the streaks).

2013 312 231 114  LC82311142013312LGN00_B8.TIF
2013 335 232 113  LC82321132013335LGN00_B8.TIF
2013 344 231 113  LC82311132013344LGN00_B8.TIF
2014 013 229 114  LC82291142014013LGN00_B8.TIF
2014 258 232 113  LC82321132014258LGN00_B8.TIF
2014 349 229 114  LC82291142014349LGN00_B8.TIF
2015 064 229 114  LC82291142015064LGN00_B8.TIF
2015 261 232 113  LC82321132015261LGN00_B8.TIF
2015 293 232 113  LC82321132015293LGN00_B8.TIF
2015 304 229 114  LC82291142015304LGN00_B8.TIF
2015 320 229 114  LC82291142015320LGN00_B8.TIF
Title: Re: PIG has calved
Post by: nukefix on November 24, 2015, 04:57:29 PM
HAIL THE POWER OF RADAR! Notice the fresh new cracks that are only visible in the B-channel looking deep blue while new cracks that no not appear in the first R-channel are cyan. Pretty stuff!

24 days between acquisitions shows the movement of the cracks but only from a close-up. Movement is very slow at the tips of the cracks and faster in the middle of the ice-stream.

This is UTM 10m pixel size (could not make Polar Stereo to work in SNAP). Sentinel-1 IW RGB of the following dates:

R= 11.9.2015
G= 5.10.2015
B= 29.10.2015
Title: Re: PIG has calved
Post by: solartim27 on November 24, 2015, 07:34:17 PM
The pinned berg is showing a good bit of rotation on todays world view.

Meanwhile, in case you've missed the Thwaites thread, there's going to be some more calving there soon, and the big berg off of there is moving out.  Here are two of the same gifs from Oct 24 to Nov 11, one should animate, and one is saved full size (2.7 Mb) if you want to zoom in closer.
Title: Re: PIG has calved
Post by: A-Team on November 24, 2015, 09:47:48 PM
could not make Polar Stereo to work in SNAP
Awesome. What UTM zone, bro?

Be a good idea to write ESA help desk about their SNAP tool not working in PS Antarctica.

Note Landsat is posting as polar stereographic if the scene's center latitude is less than -63ºS, whereas the recommended use is UTM north of -80º and PS only from there to the pole, whereas the center of Pine Island trunk is something like -77.3º, -97.5º. So if only Landsat could fall in line, we have all the coastal cryosphere in a UTM.

Google Earth UtM is saying zone 14, C 536453 m, E 1641157 m (relative to what?). We should supply EPSG codes as that is really what most software is looking for in terms of specs.

We have come a long way since Sputnik-1? That was 4 Oct 1957, over 58 years ago. These projections and more were already in use by the pharaohs.

[Edit: 3rd image is upper corner of nukefix's 10 m 3 day color interferogram displayed at 1000 ms with last frame duplicated. 4th image just animates the BGR as grayscales at 320 ms. It is amazing how l.i.t.t.l.e changes in these images over these 48 days.]
Title: Re: PIG has calved
Post by: nukefix on November 25, 2015, 09:31:08 AM
It's UTM zone 14 (auto determination).

Interesting that the new cracks can also be created in a fan-like shape. The big one appearing in the animation is about 500m wide after fanning out for 2.4km.

Here's a nice feature from the shear-zone...crevasses are formed, bent and finally they disappear, at least from sight..



Title: Re: PIG has calved
Post by: A-Team on November 25, 2015, 02:37:19 PM
It's UTM zone 14 (auto determination).
Even though in the overall Sentinel image (third image in #458) the ice shelf, calving front and lower trunk are in UTM zone 13?

There is an astonishing amount of information in these images about differential motion of various parts of the trunk (and the stress field implied by that motion). No question in my mind, Sentinel greatly outperforms published velocity products in terms of detail and accuracy.

Looking at the motion in the hair-dresser region (first image #458) by shifting the earlier date to the left until the difference (grayscale subtract) with the latest image was minimized, it appears that 6 pixels (60 m) is the best fit over the 48 day interval (1.25 m per day or 456 m per year) for the central and lower part of the image. This is slower than we were thinking but this region is on the periphery of the trunk where the velocity is falling off to zero.

The new 'crevasses' opened to a width of 430 m yet this had no impact whatsoever on the overall dimensionality despite the 660 m stretch in the direction of motion, suggesting that these new lineations were merely newly exposed (in the sense of becoming reflective to Sentinel radar) rather than newly created, melt season starting and all that.

Best cloud-free Landsat-8 matches to Sentinel-1A dates above are quite favorable for first and last:
                 
LC82321132015261LGN00 18 Sep 15  11 Sep 15
LC82321132015293LGN00 20 Oct 15  05 Oct 15
LC82291142015304LGN00 31 Oct 15  29 Oct 15
LC82291142015320LGN00 16 Nov 15


Note there's no need to restrict to 3 Sentinel dates because of only 3 color channels. From a chronologically order stack of Sentinels, any size, it's easy to make a rolling RGB image from each consecutive triplet. There is another option (less clutter) of just using pairs for RG and setting B to a favorable uniform gray. However for animation purposes it may be better to leave them as grayscales.
Title: Re: PIG has calved
Post by: nukefix on November 25, 2015, 03:38:18 PM
Looking at the motion in the hair-dresser region (first image #458) by shifting the earlier date to the left until the difference (grayscale subtract) with the latest image was minimized, it appears that 6 pixels (60 m) is the best fit over the 48 day interval (1.25 m per day or 456 m per year) for the central and lower part of the image. This is slower than we were thinking but this region is on the periphery of the trunk where the velocity is falling off to zero.
There no discernible movement at all at the tips of the "hairs". The image is resampled at 10m so even a 5m movement should show up as tinted edges of the hairs. It's all just white in the RGB.

The new 'crevasses' opened to a width of 430 m yet this had no impact whatsoever on the overall dimensionality despite the 660 m stretch in the direction of motion, suggesting that these new lineations were merely newly exposed (in the sense of becoming reflective to Sentinel radar) rather than newly created, melt season starting and all that.
I have to disagree with that, there's no sign of features getting buried/exposed on the whole 170km * 250km coregistered frame that I have (dry snow does not impede radar-waves much). A simple explanation is that these are really "hairline" cracks and possibly much smaller than the resolution-cell. Since the radar is penetrating rather deep into the ice even a deep vertical 30cm-wide crack should be clearly visible on the SAR image due to the created ice-air interface. Also due to deep penetration the image of the crack can be distorted in the SAR image leading to misinterpretation.

The optical images should be useful in inferring what is the real surface-width of the crack.
Title: Re: PIG has calved
Post by: A-Team on November 25, 2015, 11:09:32 PM
October 31 southern hemisphere corresponds to 52 days before austral midsummer solstice or April 30th in the northern hemisphere; the latitude of Pine Island calving front is not too different from Jakobshavn which would be in early melt; the iSTAR traverse of Antarctica www.istar.ac (http://www.istar.ac).u experienced milder weather than I ever saw as a paperboy during Chicago winters; the dielectric constant of wet snow or liquid water makes it impenetrable to Sentinel radar.

The first image below just is just catch-up on location maps of the 10 m forum scenes relative to the overall Pine Island trunk. The second shows the movement of the shear zone over the same dates as above which is that of a rigid body over the 48 day span of the animation. The third shows 10 Nov 15 posted as is by Wipneus which is very very similar in its details to the 31 Oct 15 Sentinel as posted in UTM14S by nukefix.

There are a great many curious features in this large complex glacier. The fourth image just shows one of this at the bottom; this area has not yet been posted at 10 m.
Title: Re: PIG has calved
Post by: A-Team on November 25, 2015, 11:42:05 PM
Here is Landsat bumped to 10 m resolution showing same flow entrainment region of #461 (29th Oct extracted) but in PS rather than Mercator projection. On a clear day (not common for the PI trunk), Landsat is quite impressive. I'll add the other Landsat counterparts in a bit. Both images need a click to see at full resolution.
Title: Re: PIG has calved
Post by: Wipneus on November 29, 2015, 04:21:25 PM
For the PIG, the 26th of November was a fantastic day. Fine weather after weeks of thick clouds and not one but two Landsat 8 passes! The first one is during the local Austral (near) summer night and the second as usual at the local morning. That is 6:50 and 14:58 UTC.

 I made an animation of the two images (45m/pix).

The nightly image has a solar elevation of only 5.7o. Shadows are long so features that otherwise (the day image with a sun elevation of 29 degrees) are difficult to see.
The new crack can now be estimated to be about 130m wide, wider  than last years crack at this time. In front of the crack two more shallow dents are visible, also been seen on Sentinel images. They lack the sharp features of the crack so they may be different.
A minor calving seems to be happening just at the bottom of the images, not visible in the day image or in any recent Sentinel image.

(must click to start).
Title: Re: PIG has calved
Post by: oren on November 29, 2015, 08:12:54 PM
Fantastic images indeed.
It's amazing how much different the image looks when the sun angle is low. So many things jump out, it's almost 3-D.
Title: Re: PIG has calved
Post by: A-Team on November 29, 2015, 09:43:38 PM
That would be 5.7º sun elevation on LC81551312015330LGN01. That image is a beauty. Below, some benefit to maybe working the contrast over with 'Integral Image Filters' in Image J --> normalize local contrast, block size 45, 1.75 std devs followed by 'Feature J" first derivative in y direction. Have to wait and see if this really has found a new crack in the making. The main crack appears a bit longer than it does in Wip's natural color pan-enhanced.

The other image of the same date LC80021132015330LGN02 only covers lower Pine Island. It is a bit of an oddity in terms of sun azimuth. Between the two of them, there is a lot of information about local topography in the shadows. However this would already be known better from lidar and stereo photogrammetry.

Sun Elevation    29.0º  vs 5.7º
Sun Azimuth      61.4º  vs 172.6º

The second image below  (from first scene, bumped to 10 m) shows a shear zone about mid-trunk where the faster moving ice stream is warping slower adjacent flow, to the point of lineation discontinuity. We've looked at this region before with both radar and panchromatic in #465 but this is the clearest view to date.

The third image shows a very pervasive and peculiar feature that seems to represent wind-driven snow. These originate in all cases from a small hole or defect on one of the lineations and extend for ~200 m to the north (bottom of image) as an elongated snowdrift. (Dry snow deposits and sun shadows don't show on radar.) PI has tens of thousands of these. By all accounts, it is very windy there; katabatic winds would blow consistently down the trunk to the coast.

Note these snow streaks are all aligned south to north, irrespective of flowline which is oblique to this axis in the example scene shown. Nonetheless, the streaks always originate as a dark spot associated with a lineation.

This Landsat in fact is not so favorable for imaging the upper trunk -- it appears that either new snow or wind-blown redistributed snow has obscured detail on the mid and upper trunk. However in the fourth image, you can see there is a whole lot going on with this glacier that needs interpretation: zones of differential speeds, over-writing of past stress fields, marginal interactions, tributary contributions getting sorted out, and so forth.

Some of this history may reveal tele-effects of recent changes down at the disintegrating ice shelf that are propagating up-trunk; others are just the consequence of buried landforms, gravitational gradients, and tributary speeds, volume and geometrical relations.
Title: Re: PIG has calved
Post by: tombond on November 29, 2015, 10:53:39 PM
Wipneus and A-Team, thank you so much for the fantastic images they are much appreciated!
Title: Re: PIG has calved
Post by: A-Team on November 30, 2015, 03:24:20 PM
Pine Island ... hmm, no island of that name in Amundsen Bay, no trees in sight -- the only vascular plants in Antarctica are Daeschampsia antarctica (hairgrass), from a genus of facultative wetland grasses, and Colobanthus quitensis (Antarctic pearlwort) in the Caryophyllaceae.

No one has the slightest idea why these and only these two species have colonized Antarctica. They do not have any specific adaptations to the Antarctic climate at either the morphological or genomic level. There's a nice review of the whole situation at http://www.scirp.org/journal/PaperDownload.aspx?paperID=7595 (http://www.scirp.org/journal/PaperDownload.aspx?paperID=7595) (

Poa annua, an annual grass, has made some recent inroads due to increasing tourism. Some tour companies have made laudable efforts to require boot washing in chlorine bleach; however shoes are not a common route of seed transportation compared to cuffs and pockets; dilute bleach would have no effect on seed viability (it is commonly used as a seed rinse prior to storage).

It turns out Pine Island Glacier is named after a US Navy sea plane tender ship, the Pine Island, that supported Antarctic mapping during Operation Highjump in 1946. The ship was decommissioned for the last time in 1972, sold to Zidell scrapyards in Portland and the metal recyled into a barge.

The ship was NOT named after Pine Island (off Ft Myers, west coast of Florida) but rather Pine Island Sound in which Pine Island resides. (The only other 3 ships in this class were named for Currituck Sound, Norton Sound and Salisbury Sound.) The correct name however is USS Pine Island, not USS Pine Island Sound.

According to wikipedia, a sound (Sund in Scandavian) is a large sea or ocean inlet larger than a bay, deeper than a bight (a bay that can be left in a single sailing tack), and wider and different in origin from a fjord; or a narrow sea or ocean channel between two bodies of land. There is little consistency in the use of 'sound' in English-language place names. Below is the namesake sound for which Pine Island Glacier is named. It is very shallow throughout, 1-2 m in depth at mean high tide. I last visited the sound in 2011.
Title: Re: PIG has calved
Post by: sidd on December 01, 2015, 06:24:08 AM
This reply is tardy, mea culpa. In post 408, the question was raised as to the concavity/convexity of surface profile. This tickled my neuron, but i had not the time to track down the reference until now.

doi:10.1002/jqs.2683

Fogwill etal. use PISM, which i am partial to, and UVic for ocean, and address the contribution of EAIS to Eemian sea level high stand, and putative weaknesses of EAIS basins today. But the particular passage which strummed my neuron was:

"We propose that the sensitivity of these sectors of the ice sheet relates to two major factors: firstly the coincidence of EAIS basins with concave ice-sheet surface profiles; secondly, the basins’ connectivity to the ocean. The basins’ bed topography and ice-sheet geometry control the mass flux from the ice sheet; those which have a weak or sliding bed have a faster flow regime, resulting in a concave surface profile (Cuffey and Paterson, 2010). In contrast, basins where ice is flowing slowly with little or no basal sliding exhibit a parabolic, or convex, surface profile and much lower ice fluxes. Our results imply that basins with concave surface profiles are particularly susceptible to ocean forcing, bringing about greater rates of surface lowering than in other areas ..."

Perhaps we should talk some more about Fogwill(2014) in an EAIS thread.

sidd
Title: Re: PIG has calved
Post by: A-Team on December 01, 2015, 01:29:11 PM
There's a lot of data out there on surface elevation of Pine Island and how it has changed over the years. The first two images illustrate the situation  a few years back at a mid-trunk transect. The bottom image shows the surface and bedrock along a 2014 longitudinal profile through the lowest point of the transect. There are convex, concave and indeterminate regions. PISM calls for some ice piracy from Filchner–Ronne and Ross.

Spatio-temporal analysis of surface elevation changes in Pine Island Glacier, Antarctica, from ICESat GLAS data and ERS-1 radar altimeter data
U Herzfeld B Farley
Annals of Glaciology 55(66) Nov 2013
Characterized by fast movement, low surface slope and grounding below sea level, Pine Island Glacier (PIG) plays an important role in the stability of the West Antarctic ice sheet. In previous work, we reported that the spatial distribution of 1995–2003 surface lowering in PIG suggests an attribution of changes to an internally forced process in the glacier. Other work associates changes in PIG entirely with processes in its ice shelf. Here time series of maps of surface elevation change in PIG and its ice shelf are derived from geostatistical analysis of ICESat GLAS and ERS-1 radar altimeter data. Based on spatio-temporal analysis of 1995–2007 elevation change, we discuss indications of processes that initiate from changes in the ice shelf versus processes that start internally in the glacier. Thinning rates continued to increase after 2003, regionally to >15 m a–1. The initiation of acceleration occurred in the interior of the ice stream, while in later years largest elevation loss was driven by changes in the ice shelf and upward propagation. By 2006, the region of thinning had expanded up-glacier beyond the initial areas of surface lowering to 100 km above the hinge line. More than one process causes dynamically complex changes in PIG

Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin
J Feldmann, A Levermann
http://www.pnas.org/content/112/46/14191 (http://www.pnas.org/content/112/46/14191) ($10 paywall Nov 2015)

Recently satellite observations and high-resolution simulations have suggested the initiation of an ice-sheet instability in the Amundsen Sea sector of West Antarctica, caused by the last decades’ enhanced basal ice-shelf melting. Localized destabilization will yield a full discharge of marine ice from West Antarctica, associated with a global sea-level rise of more than 3 m unless the ice loss is limited by ice dynamics and topographic features. Here we show that in the Parallel Ice Sheet Model PISM at 5-km horizontal resolution, a local destabilization causes a complete disintegration of the marine ice in West Antarctica. Thereafter, the marine ice-sheet instability fully unfolds and is not halted by topographic features. In fact, the ice loss in Amundsen Sea sector shifts the catchment's ice divide toward the Filchner–Ronne and Ross ice shelves, which initiates grounding-line retreat there. Antarctica will irrevocably contribute at least 3 m to global sea-level rise…

IceBridge Surveys More of West Antarctica 2014 and 2015: [no link to actual data]
The next morning, Nov. 6, mission planners returned to the Punta Arenas weather office to find that things still looked good in the Pine Island Glacier region. With a good forecast in hand, the team took off for a survey to collect data on tributaries feeding into the main trunk of Pine Island Glacier. This repeat of a survey last flown in 2010 was designed to measure changes to the ice surface beyond IceBridge’s other Pine Island Glacier missions.

On Nov. 7, favorable weather conditions were still holding in West Antarctica, so the IceBridge team headed out for a survey of the Thwaites, Smith and Kohler glaciers. This flight repeated parts of a survey flown in 2012 and primarily measured ice elevation in this rapidly-changing part of West Antarctica. In addition, researchers were able to collect high altitude sea ice elevation data with the onboard laser altimeters on the way to and from the survey area.
Title: Re: PIG has calved
Post by: A-Team on December 01, 2015, 01:52:39 PM
Here is what we are aiming for with Pine Island -- a modern representation of surface and bedrock. Unfortunately this is Store Glacier in west-central Greenland, from Project Safire http://www.spri.cam.ac.uk/research/projects/safire/ (http://www.spri.cam.ac.uk/research/projects/safire/)  Animations like this can also be done as .mov with a slider but are best viewed as a 3D graphic with handles (as in ImageJ) that can be redrawn to any perspective, with the top surface animated to show thinning, velocity and change in velocity. This would take ten minutes to do for Pine Island were it not for the obtusity with which the data is stored.
Title: Re: PIG has calved
Post by: A-Team on December 01, 2015, 09:35:22 PM
I located a nice GeoTiff of Antarctic surface elevation at 1 km horizontal resolution from V Helm et al www.the-cryosphere.net/8/1539/2014/ (http://www.the-cryosphere.net/8/1539/2014/) that they stored at the Pangaea repository http://doi.pangaea.de/10.1594/PANGAEA.831392 (http://doi.pangaea.de/10.1594/PANGAEA.831392)

This is the right way to do it, all too rare. GeoTiff has plenty of precision and its header carries along all the metadata anyone would need. You can see at a glance what the data looks like, stack as a multi-tif, process as needed and crop out the region of interest. ImageJ has a clever interactive 3D surface plot tool from which this rough animation of Pine Island surface elevation could be made.

Google topic, Find article, locate its data link --> do something, upload the product to forum: 10 minutes, not 10 hours of thrashing around in netCDF or 10 days waiting for an author to maybe respond to an email request. Now if only I could find something similar for ice thickness or bedrock and velocities ...

Title: Re: PIG has calved
Post by: AbruptSLR on December 01, 2015, 09:48:15 PM
ImageJ has a clever interactive 3D surface plot tool from which this rough animation of Pine Island surface elevation could be made.

Very nice 3D image.  I will be interesting to see if/when cliff failures occur if/when the PIIS calves away, leaving a bare & relatively steep cliff face.
Title: Re: PIG has calved
Post by: A-Team on December 02, 2015, 03:11:13 AM
Good point. It gets steep there in a hurry, slope attached (derived from V Helm DEM of 2013 via D Tschumperlé's G'MIC). I wonder what the history of the steep section is, presumably ice from the five tributaries held back at the funnel making it thicker there but thin at the shelf.

A lot of effort is expended on obtaining accurate elevation maps, not to get height about sea level, but to get at slopes, in particular to get the gradient or direction of maximum slope. Glaciers flow because of a gravitational force gradient; an ice cube sitting on a table melts but does not flow.

On a digitized DEM (a scalar field or 0-tensor representable by a grayscale), that will involve subtracting pixels in all directions from a given pixel so the error bars need to be small for this to work. The resulting derivative is a vector field (or 1-tensor) requiring two grayscales for its representation, one for magnitude and the other for direction. The Glen flow law governing glacial rheology uses invariants of 2-tensors derived from ultimately from the gradient vector field.

The three images below illustrate the issues. The first is the experimental surface elevation data cropped to PI out of a much larger map (6669 × 6669 pixels) of all Antarctica compiled by V Helm et al as finalized on 01 Sep 2013 and archived as a 170 MB 32-bit geotif at Pangeae (along with the associated error map).

The second image has calculated the gradient, determined its magnitude at each point, re-scaled those values to a 0-255 range of grays that can be displayed on a computer monitor, drawn contours connecting slopes with the same value, and displayed direction via brightness along these contours, using one of the 305 online image processing tools at https://gmicol.greyc.fr/.

The third image uses the color wheel to tint the contours of the second image to indicate direction. This direction corresponds to flow of rainwater over the surface, often but not necessarily the direction of flow of glacier ice. That flow will be orthogonal to the contours, hence their utility.

For purposes of glaciological computations within a GIS stack, two grayscales suffice: one for the magnitude of the slope and another for compass direction (no derived contouring). These grayscales would retain the bit depth appropriate to the precision of the original experimental data, as degraded by error and processing.

For example if the elevations ranged from sea level to 512 m and were known to the nearest meter, 8-bit images would be inappropriate as their 256 levels could only distinguish 2 m intervals. Here 9-bit would work satisfactorily though these would take up 16-bit given computer memory architecture.

On the other hand, 32-bit tifs are totally excessive as they can distinguish 232 = 4 294 967 296, over 4 billion values which in our example works out to 0.19 microns in a situation where random experimental error might be a meter or more. While there's no gain here, there's no harm done either with 32-bit. Other data or derived products might require it and bit depth can always be dropped at the end when all calculations have finished..
Title: Re: PIG has calved
Post by: A-Team on December 02, 2015, 01:53:48 PM
The original article shows not only surface elevations for the Antarctic continent but also slopes in degrees (Fig.6 of www.the-cryosphere.net/8/1539/2014/ (http://www.the-cryosphere.net/8/1539/2014/) ) at an author-supplied resolution of 1917 x 2179 pxls. (Images in pdfs should not be copied by screenshot but rather imported by software like ImageJ or Gimp that can extract the full native resolution supplied to the publisher.)

The legend on that figure is very instructive: Antarctica is so very flat that the greatest slope encountered (at this resolution) is 1º. For comparison, the steepest road in the world (Baldwin Street in Dunedin, NZ) is 19º. It is common to have truck escape ramps on long 5º-7º slopes However a 1º slope is quite significant for a railroad bed and early trains were restricted to half that (both for power and braking).

Simply showing the magnitude of the slope in arbitrary colors is not useful. The animation below shows futile attempts to extract the underlying slope grayscale from the original coloration by decomposition into RGB, HSV, or Lab channels. None of these work, with the possible accidentl exception of the b channel in Lab (2nd frame). Alternatively, it is easy to make or find attractive palettes from which the result data is easily recovered.

You won't see the Rignot group using a nonsense palette. For example, the Pine Island velocity map above uses a simple tint in HSV in the hue channel to carry the data.
Title: Re: PIG has calved
Post by: AbruptSLR on December 02, 2015, 09:18:57 PM
The attached Terra image of the PIIS for Dec 2 2015, shows that a minor calving event occurred on the Southwest face of the PIIS.

Edit: Possibly associated with the build-up & release-of compressive stresses in this area.

Edit2: When I say the Southwest face of the PIIS; I mean the area immediately to the Northeast of the ice shelf for the Southwest Tributary Glacier.
Title: Re: PIG has calved
Post by: sidd on December 03, 2015, 02:31:39 AM
for someone who whines about basal hydrology all the time, i haven't brought up Livingstone(2013) in a while ... that might be relevant in the Greenland threads as well ...

doi:10.5194/tc-7-1721-2013
open access, so nice

fig 1 for antarctica
Title: Re: PIG has calved
Post by: A-Team on December 03, 2015, 10:50:38 AM
Pulling out the Pine Island portion of the predictions of SJ Livingstone 2013 for basal hydrology, the first frame shows a classical drainage system that corresponds fairly well with the center lines of surface tributaries. However the large lake at the upper confluence has no surface manifestation in either Landsat or Sentinel.

The lake is fairly stable to monte carlo re-sampling of the bedrock DEM with respect to its error map, second frame. The bed of Pine Island is cold according to 2010 modeling by Pattyn (still paywalled), rather than polythermal, third frame, meaning the bed is not at the pressure melting point, the streams and lake don't actually form, and rapid flow here is not primarily deformational.

Overall, the predicted basal hydrology of PI is not remarkable relative to Thwaites, Vostok, and other features of the continent. However there is little here that is experimentally testable any time soon. It may be better to stick with surface observables as change can be readily monitored over the 12 day Sentinel return window by folks at home.

There is quite a bit of new information about Pine Island emerging at conferences such as the Nov 13 ISTAR, one component of which traversed some of the tributaries with seismic, radar, and 50 m deep firn cores. It's not clear how many of these will put sufficient detail online to accompany the abstracts.

The Pine Island twitter site is the best place to look for new releases though many of the tweets are cryptic and their links dead ends. https://twitter.com/AntarcticPIG

Late glacial sub glacial lake sediments recovered and sampled in Pine Island Bay
XII International Symposium on Antarctic Earth Sciences, Goa, India, 13 July 2015 - 17 July 2015 .
G Kuhn et al

Subglacial meltwater facilitates rapid ice flow beneath concurrent ice sheets, and there is widespread evidence for a dynamic subglacial water system beneath the Antarctic Ice Sheet. It steers and affects the pattern of ice flow and is a direct result from boundary processes acting at the base of the ice sheet, i.e. pressure induced basal melting. Consequently, the occurrence of subglacial meltwater plays an important role in bedrock erosion, subsequent resedimentation, and in shaping the topography of icesheet beds.

Here we present new geological and geochemical data from sediments recovered on the West Antarctic continental shelf in Pine Island Bay that we interpret as reliable indicators for deposition in a palaeosubglacial lake beneath the formerly expanded West Antarctic Ice Sheet, presumably during or following the Last Glacial Maximum. Characteristic changes of sedimentary facies and geochemical profiles within these cores taken on RV Polarstern expeditions support the presence of an active subglacial lake system during the late stages of the last glacial period.

These findings have important implications for palaeo icesheet dynamics, suggesting there was considerable water available to lubricate the bedrockice interface and deposit water saturated subglacial sediments (soft tills).... Our findings may also have implications for ice sheet models, which have to consider the predominantly nonlinear effects related to subglacial hydrology.
Title: Re: PIG has calved
Post by: AbruptSLR on December 03, 2015, 06:25:02 PM
for someone who whines about basal hydrology all the time, i haven't brought up Livingstone(2013) in a while ... that might be relevant in the Greenland threads as well ...

doi:10.5194/tc-7-1721-2013
open access, so nice

fig 1 for antarctica

For those new to this Antarctic folder, more information on subglacial meltwater drainage systems can be found at the following link:

http://forum.arctic-sea-ice.net/index.php/topic,404.0.html (http://forum.arctic-sea-ice.net/index.php/topic,404.0.html)
Title: Re: PIG has calved
Post by: A-Team on December 03, 2015, 08:32:07 PM
The image below shows the 20 and 200 m/year velocity contours for Pine Island but there is a lot more for us in this Antaractic-wide article. We may be able to improve it locally and at Thwaites using incoming Sentinel 1A's if we can replicate Ng's procedures.

Reprojecting Sentinel 1A to 10 m UTM, two pixels of movement in scenes a year apart amounts to the 20 m/yr contour. That's within range, depending on the presence of scene markers co-moving in the ice without distortion. With this contour overlaid on the Sentinels above, we could check now for availability of markers.

The lineations don't extend this far up the tributaries but other wave-like patterns do and may be more favorable. In comparing sensitivities, recall interferometry looks at the horizontal component of line-of-sight displacement of ice to satellite over two dates whereas nadir views look at a projection of (sloped) ground displacement, and GPS (or flag) movement refers to net surface displacements in absolute coordinates, whereas tape measurements of flag position before and after refer to a lumpy, curved and sloped earth surface, with meters per year on the WGS84 ellipsoid being the site of comparison.

Spatial complexity of ice flow across the Antarctic Ice Sheet
Felix S. L. Ng   
Nature Geoscience 8  847–850 2015
doi:10.1038/ngeo2532 Published online 16 Sep 2015
 
Fast-flowing ice streams carry ice from the interior of the Antarctic Ice Sheet towards the coast. Understanding how ice-stream tributaries operate and how networks of them evolve is essential for developing reliable models of the ice sheet’s response to climate change.

A particular challenge is to unravel the spatial complexity of flow within and across tributary networks. Here I define a measure of planimetric flow convergence, which can be calculated from satellite measurements of the ice sheet’s surface velocity, to explore this complexity. The convergence map of Antarctica clarifies how tributaries draw ice from its interior. The map also reveals curvilinear zones of convergence along lateral shear margins of streaming, and abundant ripples associated with nonlinear ice rheology and changes in bed topography and friction.

Convergence on ice-stream tributaries and their feeding zones is uneven and interspersed with divergence. For individual drainage basins, as well as the ice sheet as a whole, fast flow cannot converge or diverge as much as slow flow. I therefore deduce that flow in the ice-stream networks is subject to mechanical regulation that limits flow-orthonormal strain rates. These findings provide targets for ice-sheet simulations and motivate more research into the origin and dynamics of tributarization.
Title: Re: PIG has calved
Post by: A-Team on December 04, 2015, 06:05:18 PM
I'm looking now inside the FSL Ng paper (unusual for having no co-authors), several posts on this are in the works. It covers all of Antarctica but with special blow-ups of Pine Island/Thwaites, Bindschadler/MacAyeal  Whillan/Mellor, Lambert, Larsen C (unlabelled Fig1e) and a few others but not including Toten.

The caption of Fig.1 got my attention as it states "Color scale applies to all panels [and two full-resolution Pangaea tifs] and is optimal for rendering features within streaming texture" (emphasis added).

The maps are quite unattractive visually but that could be forgiven if it was indeed highly effective. But what could optimal even mean -- how is such a thing scored, what is the next closest key scheme, how could it simultaneously be optimal at vastly different display scales and for both convergence and strain rate textures, by what methodology was this discovered, who should be credited, and above all, where else in science should this palette be deployed?

The data being displayed has an effective range of  [-1,1] up to a scalar and low enough precision that 8-bit suffices (rare in glaciology to match bin number to data precision). Although that range could be displayed as an ordinary grayscale, zero has a special meaning that would not stand out as 128 gray. The data ranges here are symmetric but otherwise similar to the needs of elevation maps ranging about sea level as zero.

Ng followed best-practices (again rare in glaciology) embedding the color scale within the figure rather than providing it as a loose supplemental figure. This means the colors used in the maps are in fact identical to those used in the key (these won't match after separate lossy jpeg compression). It also means a color picker can pull out and count exactly those pixels of a given value (or range of values), eg all the extreme strain rate locations in Antarctica.

Opening the full-resolution tifs in ImageJ showed the map to be indexed color. The LUT (lookup table that maps [0,255] --> RGB color space assignment) can be conveniently viewed, edited, swapped out for any other color table, or saved to re-color other people's sub-optimal maps. The LUT shows exactly which map colors were chosen.

Since white and its pale shades are intuitively appropriate to display less significant regions here and the parameters are inherently linear with no way-stations of significant thresholds, it makes sense to run gradients out from white to two fixed end point colors in 128 steps each and butt these back to back, which is what Ng did, using contrasting colors for the two end points (opposite colors across the color wheel). These are called diverging palettes.

So far so good, but what is optimal about this choice given the muddy non-terminal values, with shades of blue being the very worst for human eye color discrimination? In advanced perceptual palettes, gradient steps are not made in RGB or HSV but equidistant in CIELAB, which would be optimal in that experimental sense though that might not carry forward to monitor display devices very well. Here there is no strict regularity in any channel after RGB, HSL, HSV or LAB decomposition.

It's imperative to stay within sRGB, the colors that can be displayed by a monitor. Reverse image search does not find a match with a previously known palette. Matlab offers many palettes, some of them like jet and parula are fairly widely used.

It's probable some software somewhere claimed the palette here was optimal under some technical criterion for which there is no consensus. The empirical approach has proven far more effective: simply scroll rapidly through a large family of palettes to find the effective ones for a given data set, not seek to deduce an optimal palette from first principles.

http://photorealizer.blogspot.com/2012/04/colorimetry.html (http://photorealizer.blogspot.com/2012/04/colorimetry.html)
https://mycarta.wordpress.com/2012/02/09/visualization-tips-for-geoscientists-matlab/ (https://mycarta.wordpress.com/2012/02/09/visualization-tips-for-geoscientists-matlab/)
http://www.codeproject.com/Articles/243610/The-Known-Colors-Palette-Tool-Revised (http://www.codeproject.com/Articles/243610/The-Known-Colors-Palette-Tool-Revised)
http://rsb.info.nih.gov/ij/plugins/lut-editor.html (http://rsb.info.nih.gov/ij/plugins/lut-editor.html)

Here we also need to look at the streaming textural results themselves and what their inherent display issues are relative to human pattern recognition abilities. For example, the figure caption states "dashed ellipses mark convergence ripples associated with bumps/steps in BEDMAP2 topography; these often pair together to show divergence followed by convergence along flow."

A good color palette might suggest this hypothesis but is no substitute for a automatic classification regime. That would require a correlation scheme between the topography bump layer and the flow convergence layer.

It is critical not to alter palettes from the original in the process of moving them from the official archived tif and analyzing them. Here the palette, a peculiar 1600 by a reasonable 200 pixels, can be exchanged between ImageJ and Gimp, each of which has its strengths, using compressed but lossless png format. Since the palette is really only 1 row of pixels extended identically vertically, its compressed size is a mere 2 kb.

The width of an indexed color palette should always be a multiple of 256 (so that each bin has equal width). Here it is not: it should have been 6*256=1536 pixels in width. Something is therefore wrong with palette construction and placement, probably during resizing which introduces interpolation artefacts. (To extract an object like a palette, crop to a generous border, add an alpha channel, select and delete the border, use 'autocrop image' to cleanly remove blank space, obtaining a palette with no border.)

The great thing about indexed color and archiving full-resolution tifs is that the scientific reader can easily change the colors to something else without any degradation of data quality. Indexed color is also best for animations since the gif89a standard allows every frame to have its own LUT.
Title: Re: PIG has calved
Post by: sidd on December 04, 2015, 09:21:36 PM
"...2010 modeling by Pattyn (still paywalled) ..."

available at

homepages.ulb.ac.be/~fpattyn/papers/Pattyn2010_EPSL.pdf

nice paper.
Title: Re: PIG has calved
Post by: A-Team on December 05, 2015, 11:08:07 AM
sidd, thx for the full text link to Pattyn 2010. Fascinating that the first maps of basal conditions of the Antarctic ice sheet were published 52 years ago. The experimental situation on Antarctic geothermal heat has not improved much since and remains much worse than Greenland, which is abysmal but at least has potential (dense radar tracks which can yield temperature profiles: http://onlinelibrary.wiley.com/doi/10.1002/2014JF003418/full (http://onlinelibrary.wiley.com/doi/10.1002/2014JF003418/full)).

However any kind of map suffices for playground development (sharpening of techniques to be applied meaningfully at some later date). The map below suggests that Pine Island and Thwaites have quite a warm bed, though correspondence with tributary structure is disturbingly poor.

Basal conditions (temperature and hydrology) of the Antarctic ice sheet are poorly understood. Nevertheless, basal conditions govern to a large extent the dynamical behavior of ice masses. Underneath present-day ice streams and outlet glaciers of Antarctica and Greenland, water and deformable wet sediments lubricate the base, hence facilitating fast ice flow. The interaction between the ice and its underlying bed, which controls how basal velocity will change as ice sheet stresses evolve, remains a key uncertainty.

Knowledge of basal ice sheet conditions is also essential in the quest for oldest ice, which occurs where basal ice layers are frozen to the bed. Obvious places to look for are the deepest parts of the ice sheet, where ice is thick, and accumulation rates are low. However, a thick ice cover insulates very well and keeps the geothermal heat from escaping to the surface.

Direct measurements of basal temperature are limited to a small number of boreholes. Several sites neared the pressure melting point at depth (eg Vostok, EPICA Dome C, EPICA DML, Dome Fuji). Thence, we have to rely on other techniques, such as ice sheet modeling, to catch a glimpse of the sub-ice environment.

One of the earlier estimates at basal temperature conditions, Zotikov 1963, concluded the central parts of the Antarctic ice sheet are at pressure melting point. The lack of detailed measurements on surface topography and bedrock prevented a more rigorous approach and the basal temperature field remained rather schematic. However, the quality of the basal temperature distribution remains highly dependent on the distribution of geothermal heat flux. [edited]
Title: Re: PIG has calved
Post by: AbruptSLR on December 05, 2015, 05:16:39 PM
However any kind of map suffices for playground development (sharpening of techniques to be applied meaningfully at some later date). The map below suggests that Pine Island and Thwaites have quite a warm bed, though correspondence with tributary structure is disturbingly poor.

A-Team,

In Reply #26 of the Tectonic thread (see link below), I point-out that while the geothermal pattern of the figure that you provide has value, the units of the figure are so out of date as to be considered wrong by current standards.

http://forum.arctic-sea-ice.net/index.php/topic,393.0.html (http://forum.arctic-sea-ice.net/index.php/topic,393.0.html)

My wife needs me to run errands so I do not have time to point-out in which threads there is more current information about the BSB geothermal readings.

Best,
ASLR

Edit: I am temporarily back from my errand(s) & provide the following, somewhat more updated (previously posted in the " Subglacial Lake and Meltwater Drainage Systems" thread) information focused on the Byrd Subglacial Basin, BSB:

The first attached image comes from:
Dustin M. Schroeder, Donald D. Blankenship, Duncan A. Young, and Enrica Quartini, (2014), "Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet", PNAS, doi: 10.1073/pnas.1405184111

http://www.pnas.org/content/early/2014/06/04/1405184111.abstract (http://www.pnas.org/content/early/2014/06/04/1405184111.abstract)

http://www.pnas.org/content/suppl/2014/06/04/1405184111.DCSupplemental (http://www.pnas.org/content/suppl/2014/06/04/1405184111.DCSupplemental)

The second attached image comes from:
http://www.scientificamerican.com/article/high-heat-measured-under-antarctica-could-support-substantial-life/ (http://www.scientificamerican.com/article/high-heat-measured-under-antarctica-could-support-substantial-life/)

Additionally, Replies #72-73 in the "Surge of WAIS Ice Mass Loss" thread contain discussions from a couple of years ago about the subglacial drainage system in the BSB.
Title: Re: PIG has calved
Post by: A-Team on December 05, 2015, 06:19:18 PM
wife needs me to run errands so I do not have time
Ditto. End of year stuff closing down on me as well. We were only interested in that map because of its cited use as a basis of the Ng article. We can maybe use a better map to see if the results there hold up. Same for the updated Bedmap2 that  came out the other day (according to twitter, I don't have link yet to the file).
Title: Re: PIG has calved
Post by: AbruptSLR on December 06, 2015, 02:26:45 PM
wife needs me to run errands so I do not have time
Ditto. End of year stuff closing down on me as well. We were only interested in that map because of its cited use as a basis of the Ng article. We can maybe use a better map to see if the results there hold up. Same for the updated Bedmap2 that  came out the other day (according to twitter, I don't have link yet to the file).

I am not sure whether the following link leads to the Bedmap2 data that you are looking for or not:

https://www.bas.ac.uk/project/bedmap-2/#data (https://www.bas.ac.uk/project/bedmap-2/#data)
Title: Re: PIG has calved
Post by: A-Team on December 08, 2015, 03:28:35 PM
updated Bedmap2 that  came out the other day (according to twitter)
That's the correct link. I had merely come across some idiot grad student breathlessly twittering on 21 Nov 2015, urging us to drop what we are doing to check out the latest news: the 06 Mar 2013 data release of Bedmap2.
Updates to Bedmap2 - 23rd April 2013
ASCII grid dimensions: During the export process, 67-cell 'No Data' buffers were inadvertently added around the ASCII surface and bed grids, so these grid dimensions were larger than necessary (6801x6801 pixels). All files were, however, properly geolocated and the file headers correctly described the file dimensions. We have recreated these grids without the buffers so their dimensions are now 6667x6667 pixels.

Ice thickness data format: 4he geodatabase and tiff versions of the ice thickness grid were inadvertently in 32-bit integer format rather than 16 bit. We have corrected this.

Bed elevation inconsistencies: 36 pixels failed a test of consistency for bed+thickness=surface over grounded ice, or bed+thickness<surface for floating ice. We have corrected this by adjusting the bed elevation accordingly in all of the formats.

Update to Bedmap2 – 31st August 2013: Conversion of Bedmap2 height reference to WGS84 ellipsoid
The bedmap2_readme .txt file incorrectly stated that the gl04c_geoid_to_wgs84 grid should be subtracted from the Bedmap2 grids to convert to WGS84. It should be added. The readme files are being changed.
Title: Re: PIG has calved
Post by: Wipneus on December 09, 2015, 12:49:03 PM
Access to the Sentinel 1A images has been difficult, if not impossible, for the last 10 days (or since Sentinel 2A image stream has started). It is the reason for the belated availability of the 4 December IW image. It shows the grounded calving is now resisting the push from the advancing glacier and rotates rather than moves. Small calving(s) can be seen in this animation (@80m/pix) with the 22 November image. Note that the "medium" sized iceberg visible in the 22 Nov frame has its origins in the big calving this summer and has been blown back.

Title: Re: PIG has calved
Post by: A-Team on December 09, 2015, 03:00:13 PM
Access to the Sentinel 1A images has been difficult, if not impossible
I eventually got the new MS Bing-based interface to open. It is highly defective at the Ellesmere, northern Greenland, Spitzbergen latitudes. I drew a select rectangle but could not find a way to load its corners in the search box.

Astonishing really that an organization this size does not have the slightest idea how to set up a web server or provide a stable search interface for a simple database.

The visitation load being reported is not heavy as these things go. They don't seem to be mirroring which has been widely used since the mid-90's to distribute load. It appears that they are have not separated the visitor interface server from the download server.

Meanwhile, not utilizing cloud storage but rather a 'rolling archive' means a whole lot of imagery has been deleted without anyone having been able to access it. Lots more satellites to come in this Copernicus series ... they are not ready.

What I see here is computer-incompetent upper management that they are not able to fire or replace.

I've found a few cryosphere Sentinel-2A images at ESA. These are very nice but are often unlabelled as to location, image north, resolution, scale, processing level and so forth. It seems like a neat satellite with well-chosen bands but so far it is all a waste.

Since 03-Dec-2015 the main access point for the Sentinels Scientific Data Hub has been experiencing considerable performance issues. The problems are under continued investigation. To alleviate the problem a temporary access for the Sentinel-2 data has been set up for all users here: https://scihub.copernicus.eu/s2 . Please login to this service using the guest/guest account (no additional registration is needed). New information regarding the return to full service will be provided as soon as possible. 07 Dec 2015 - 17:27
Title: Re: PIG has calved
Post by: AbruptSLR on December 11, 2015, 05:42:44 AM
I will be on vacation after tomorrow morning until after Dec 20th.

ASLR
Title: Re: PIG has calved
Post by: A-Team on December 11, 2015, 01:23:25 PM
on vacation after tomorrow morning until after Dec 20th
Thx for all those excellent posts!

Some progress to report on Sentinel-2A. First, a rare image of never-studied Jungersen Glacier in extreme northern Greenland (82.1º N, -43.1º W) which flows into Nordenskiöld Fjord.

It has some similarities in its arcuate features in 3-4 places to what we've been discussing for upper Pine Island so I'm posting it here. From its features, Jungersen might appear to be faster moving than Pine Island's trunk but is actually not.

Sentinel-2A is similar to Landsat-8 but has improved ground resolution (10 m vs 15 m) for three bands in the visible and band 8 in the near infrared. It has a 10 day return which will drop to 5 when its twin sister 2B is launched. It is primarily for vegetation monitoring and no imagery will be taken beyond 83º for Antarctica.

This works out ok for Pine Island at -75.3º and other coastal glaciers. However no Sentinel-2A imagery has been released yet for any glacier in Antarctica.

ESA has done a rank amateurish job of annotating Sentinel-2A gallery images, not providing ground resolution or band combinations used. Via comparison with band 8 of Landsat-8, the Jungersen image has been inexplicably dumbed down to 15 m and so does not illustrate the full capabilities of their satellite (the entire purpose of the gallery). The image is likely comprised of bands 4,3,2 as RGB but may involve additional undescribed processing steps to correct color. (Landsat provides two tutorials on this.)

The most intriguing feature of Sentinel-2A is 3 channels at the boundary of red visible and near infrared termed the 'red edge'. There is nothing that corresponds to this in Landsat. Whether it will be useful in cryosphere work remains to be determined -- the data server remains broken and no examples have been provided in their image gallery. These are at 20 m and may not differ enough over ice to form a distinctively colored faux RGB.

Here are the bands as (peak, width, resolution):

B2 (490/65/10), B3 (560/35/10), B4 (665/30/10)
B5 (705/15/20), B6 (740/15/20), B7 (775/20/20), B8a (865/20/20)
B8 (842/115/10)

http://www.esa.int/spaceinimages/Images/2015/07/A_slippery_slope (http://www.esa.int/spaceinimages/Images/2015/07/A_slippery_slope)
Title: Re: PIG has calved
Post by: wili on December 11, 2015, 03:29:41 PM
"Thx for all those excellent posts! "

Seconded!
Title: Re: PIG has calved
Post by: Wipneus on December 13, 2015, 01:02:46 PM
Conditions for landsat imagery on the 12th December where almost as good as those one cycle (16d) ago, described in post #466. Elevation of the "mid-night sun" is 7.84 degrees. Here is a detail of those nightly images at a resolution of 15m/pix showing some calving activity in "the notch".

(click to animate)
Title: Re: PIG has calved
Post by: crandles on December 13, 2015, 01:45:28 PM
Has the calved iceberg's rotation stopped? Would you expect that once it has rotated, as it has, for it to continue to rotate as it is pushed or is it just as likely to stop and start such rotations? Does this depend mainly on how many places it is grounded at or strength and thickness of ice being driven into the grounding points or other factors?
Title: Re: PIG has calved
Post by: Wipneus on December 13, 2015, 03:07:41 PM
Has the calved iceberg's rotation stopped? Would you expect that once it has rotated, as it has, for it to continue to rotate as it is pushed or is it just as likely to stop and start such rotations? Does this depend mainly on how many places it is grounded at or strength and thickness of ice being driven into the grounding points or other factors?

There is about 0.5o rotation between the images. Movement (in a straight line) with the glacier seems to dominate again. I looked at all the cracks visible in that iceberg and cannot see anything changing: no internal stress is building up. So it may be grounded, but it is not sticking.
Title: Re: PIG has calved
Post by: Wipneus on December 14, 2015, 08:30:27 AM
Forward movement and rotation can be judged by coding with different colors, Red for 12Dec, Green for 26Nov.

(click for a larger image)
Title: Re: PIG has calved
Post by: oren on December 25, 2015, 12:10:13 PM
Forward movement and rotation can be judged by coding with different colors, Red for 12Dec, Green for 26Nov.

(click for a larger image)

Thanks Wipneus. Great way of showing the movement.
Title: Re: PIG has calved
Post by: Wipneus on January 06, 2016, 08:58:53 AM
In this sequence, 24 Dec - 4 Jan, the "camera" moves with the advancing glacier. This highlights the slight rotation of the "grounded" calving. Two minor calving can be seen that can separate at any time now. Note that the images are not from the same orbital position ( no exact multiple of 16 days  separation), not really useful to detect small changes in crack widths/lengths.

(click required)
Title: Re: PIG has calved
Post by: oren on January 06, 2016, 10:46:08 AM
Beautiful
Title: Re: PIG has calved
Post by: Wipneus on January 08, 2016, 03:56:10 PM
View of the "crack" with different solar lighting. The 4 Jan image (same as in the previous post) is acquired during the "nightly" semi orbit of the Landsat satellite. Sun elevation is only 7.5o, in the image the light is from the right. The 6 Jan image is taken during the "day", with sun elevation 29.5o, light comes from the top-left, about the 11 o'clock position.

The low sun gives a dramatic better view on the crack, showing depth where the other does not and shows it extending much further.

Landsat ID's: LC81561312016004LGN00 (4 Jan) and LC80011132016006LGN00 (6 Jan).

Click to see in 7.5 m/pix resolution
Title: Re: PIG has calved
Post by: Wipneus on January 10, 2016, 11:54:48 AM
The minor calving at the PIG front has taken place, sometime between 6 and 9th of January. Again a sequnce moving with the glacier, so we see the stationary rocks and ice moving backward and see the big grounded calving rotate.

Click to see the 30m/pix aniamtion.
Title: Re: PIG has calved
Post by: A-Team on January 22, 2016, 02:09:06 PM
By exploiting the greater bit depth and massively processing all possible image pairs, Landsat-8 can provide an alternative to radar interferometry in providing velocity maps of Antarctica. A new continent-wide Antarctic mosaic is ready but not yet released. However the ‘methods’ paper is out and very instructive. Pine Island Glacier furnished one of the examples, see below.

Because they also did processed Greenland (indeed all land ice globally), I’ve discussed other parts of the paper in three posts to the Store Glacier forum, links below.

People on these forums have measured ice velocity from time to time but not at the extreme sub-pixel levels achieved here. The figure shows speed for a 32-day Landsat-8 band 8 scene pair from Pine Island (longer time separations are used in slower areas). Note the orange asymmetry (white arrow) in the transition from fast red to slow green; this seems not to be an artifact but detected by SAR as well (2nd image).

2.5. Sub-pixel offset determination

To facilitate accurate displacement measurement, we take advantage of the tendency for ice sheet and glacier images to have a smoothly varying correlation surface in the vicinity of a valid match. We use a bivariate cubic spline to fit the peak in the integer-pixel offset correlation surface, and then find the sub-pixel location of the peak of this spline. For computational efficiency, we perform a maximum gradient search of this splined surface in the gridded x and y directions, locating the peak to within ~0.01 pixel.

The resulting offset fields show smoothly varying values, suggesting that the data are not being overfit. Fig. 6a shows the flow speed over Pine Island Glacier in Antarctica, while Fig. 6b shows only the sub-pixel part of calculated offsets. With only the fractional component of the y pixel offset shown, values in this figure wrap at ±0.5 pixels [ie fractions amount to mod 1 modular arithmetic similar to phase wrapping], producing an appearance similar to a differential SAR interferogram. The smoothly varying sub-pixel displacement field, particularly in the slow-moving areas, demonstrates the fidelity of both the internal image geometry and the derived offsets.
Rapid large-area mapping of ice flow using Landsat 8
M Fahnestock, TScambos, T Moon, A Gardner, Terry Haran, Marin Klinger
http://www.sciencedirect.com/science/article/pii/S003442571530211X (http://www.sciencedirect.com/science/article/pii/S003442571530211X) open access

Previous commentary:
http://forum.arctic-sea-ice.net/index.php/topic,1462.msg68479.html#msg68479 (http://forum.arctic-sea-ice.net/index.php/topic,1462.msg68479.html#msg68479)
http://forum.arctic-sea-ice.net/index.php/topic,1462.msg68593.html#msg68593 (http://forum.arctic-sea-ice.net/index.php/topic,1462.msg68593.html#msg68593)
http://forum.arctic-sea-ice.net/index.php/topic,1462.msg68662.html#msg68662 (http://forum.arctic-sea-ice.net/index.php/topic,1462.msg68662.html#msg68662)
Title: Re: PIG has calved
Post by: solartim27 on January 26, 2016, 09:52:02 PM
More minor calving on either side of PIG, as well as a bit of advance.  Dates are from Jan 14 to Jan 26.  Thwaites seems to advance a similar amount in the Sentinel image, but I did not notice any new calving there.
Title: Re: PIG has calved
Post by: Wipneus on January 27, 2016, 09:11:56 AM
In the animation a remarkable darkening of the whole 26 Jan image can be seen. Darker images started mid January, at about the same time that the optical images (MODIS, Landsat) show thick cloud cover.
So are we looking at the effects of clouds/assumed precipitation on Sentinel's 1A radar? Something changing in the processing?
Title: Re: PIG has calved
Post by: nukefix on January 27, 2016, 10:25:47 AM
It's difficult to say whether Polarview-processing has changed with respect to contrast-stretching. Wet snow has a very low backscatter as it absorbs the radar waves very well. Limited surface-melting should be possible at this time of the year, right?
Title: Re: PIG has calved
Post by: Wipneus on January 27, 2016, 10:50:15 AM
It is not Polar View, it is visible from unprocessed image downloaded from the data hub as well.
Further, I have seen it before. A  couple of months ago, perhaps October cannot be sure, also with PIG images and visible clouds in the optical data.
Title: Re: PIG has calved
Post by: solartim27 on February 05, 2016, 08:57:40 PM
Major rotation of the pinned berg.  Something is going on under the clouds.
Title: Re: PIG has calved
Post by: AbruptSLR on February 05, 2016, 10:32:12 PM
Major rotation of the pinned berg.  Something is going on under the clouds.

Nice catch!  I agree that it looks like something is happening under the clouds offshore of the PIIS.  The first attached image shows the Earth Surface Wind & MSLP map for the Amundsen & Bellingshausen Sea areas for Feb 4 2016, showing a large low pressure system causing a wind pattern contributing to local ocean upwelling, while the second image shows the Earth Ocean Current & SSTA map for Feb 5 2016 showing a large area of warm upwelled water right offshore of Pine Island Bay.  The third image shows a Landsat 8 image of the area offshore of Thwaites for Feb 5 2016, showing a major fracturing of much of the fast sea ice in this area; which could be due to a combination of strong winds and local upwelling of warm CDW.  This combination of recent local atmospheric & oceanic conditions could be contributing to basal ice melting for both the PIIS & the pinned iceberg in-front of the PIIS.
Title: Re: PIG has calved
Post by: AbruptSLR on February 06, 2016, 09:10:13 PM
The attached Aqua image for Feb 6 2016, confirms that not only has the pinned iceberg rotated, but it has also translated away from the calving face of the PIIS:
Title: Re: PIG has calved
Post by: Wipneus on February 07, 2016, 05:43:41 PM
Today's Sentinel 1A image is the first after the rotation event, on the previous image from 2 Feb nothing is visible.
Here is an animation composed of today's image with the one 12 days before.

(yes, a click will get it going)
Title: Re: PIG has calved
Post by: Wipneus on February 12, 2016, 09:08:32 AM
A small break from the main grounded ice berg. Here I took Sentinel images from 10 and 12 February, rotated and moved them for approximate alignment and created a color image using Red=10 Feb and Green=12 Feb. The berg falls slightly outside the 10 Feb image, so on the right only the green color is available.
Title: Re: PIG has calved
Post by: oren on February 12, 2016, 04:01:01 PM
Maybe this stubborn berg got tired of sticking around for so long, and decided to break up piece by piece?
Title: Re: PIG has calved
Post by: Wipneus on March 01, 2016, 05:56:47 PM
In this animated sequence of two Sentinel 1A images, not only the glacier front is advancing. Looking closer, the grounded iceberg has made a tiny clock-wise rotation.

Must click for that.
Title: Re: PIG has calved
Post by: steve s on March 01, 2016, 09:13:04 PM
Thanks Wipneus; the sequences are always interesting. In this case, the ongoing forces on the separated berg seem impossibly strong.

Probably something I am missing in the way of force transmission, but the glacier's movement seems to remain correlated with the bergs rotation although the two are physically separated with the berg pinned. The forces on the berg are sufficient, whatever their sources, to cause rapid growth of peripheral crevasses and so on. If a river were flowing beneath the glacier generating the forces, it would have to be a very vigorous river. I think that can be ruled out.

Any ideas?
 
Title: Re: PIG has calved
Post by: AbruptSLR on March 01, 2016, 09:39:43 PM
Thanks Wipneus; the sequences are always interesting. In this case, the ongoing forces on the separated berg seem impossibly strong.

Probably something I am missing in the way of force transmission, but the glacier's movement seems to remain correlated with the bergs rotation although the two are physically separated with the berg pinned. The forces on the berg are sufficient, whatever their sources, to cause rapid growth of peripheral crevasses and so on. If a river were flowing beneath the glacier generating the forces, it would have to be a very vigorous river. I think that can be ruled out.

Any ideas?

It's not a river but rather the advection of CDW into and then out-of the sub-ice shelf cavity, and which is concentrated in the area of the iceberg.
Title: Re: PIG has calved
Post by: steve s on March 01, 2016, 10:09:33 PM
Thanks ASLR.

I was originally thinking of tides being too weak. Now I realize that the specific gravity of warm water is higher than of cold, so the warm basal waters become an outflow river at the lower surface of the glacier. The strength of the flow (surprises me) is made visible by the ongoing separation between the berg and the glacier. 


Title: Re: PIG has calved
Post by: sidd on March 01, 2016, 10:59:13 PM
" ... the specific gravity of warm water is higher than of cold ... "

wait, what ?
Title: Re: PIG has calved
Post by: AbruptSLR on March 01, 2016, 11:36:37 PM
" ... the specific gravity of warm water is higher than of cold ... "

wait, what ?

The first image shows that the advected warm CDW melts ice at the grounding line, which then due to its low salinity has a low density (even though it is cold) flow up and out of the Pine Island Ice Shelf, PIIS, where it would hit the iceberg.

The second image shows the measured water velocities beneath, and existing from beneath, the PIIS, for both the 2009 (panel C) and the difference from 2009 to 2012 (panel D); which confirm that the water velocities near the iceberg are meaningful.

I note that wind advects the warm CDW moves over the continental shelf into a deep trough that directs the warm CDW beneath the PIIS by a combination of momentum and the siphon effect of the melted ice at the grounding line and basal ice melt from the bottom of the PIIS.

Edit: For circulation pattern see:
http://nora.nerc.ac.uk/502263/1/1244341RevisedManuscript2.pdf (http://nora.nerc.ac.uk/502263/1/1244341RevisedManuscript2.pdf)

Caption for second image: "Fig. 3. Observed and simulated hydrography and circulation in 2009 and 2012. A. Section of observed and simulated 2009 potential temperatures (color) and salinity (black contours) along the eastern Amundsen Sea trough and underneath the PIG ice shelf. White lines show the surface-referenced 27.47 and 27.75 isopycnals. The panel shows observations outside the PIG cavity, and simulation results within it. Observations are linearly interpolated from profiles (black triangles) indicated in figure 1B. B. Same as A but for the 2012 observations and simulation. C. Modeled potential temperature (color) and velocity (black vectors, every fifth vector is shown) averaged within 50 m of the seabed for the 2009 simulation. White vectors show the corresponding velocity observed by Autosub (binned on the model grid, see also Fig. S2A). The cyan line indicates the position of the section used in panels A and B. The white line indicates 750 m seabed depth. D. Same as C but for the difference between the 2012 and the 2009 simulations."
Title: Re: PIG has calved
Post by: steve s on March 02, 2016, 09:54:52 AM
" ... the specific gravity of warm water is higher than of cold ... "

wait, what ?

Sorry I was imprecise Sidd. Fresh water's density is greatest at about 4 degrees C, so ice forms at the water's surface, where the water is at 0 degrees. Dissolved salt depresses the freezing point and increases the density, but leaves the general relationship unchanged.

Advective outflows, having lost heat to the ice, are less dense and above the inflows. The density change is due to both cooling and freshening.

The motion of the berg indicates that a large volume water is traveling at the top of the water column -- along the bottom of glacier. To my amateur eye, the strength of the outflow at the top of the water column seems either (1)  too great to be explained by melt-water alone (as ASLR's figure suggests is the case); or (2) the volume of melting is higher than seems to be indicated by apparent volume changes in the glacier.
Title: Re: PIG has calved
Post by: AbruptSLR on March 02, 2016, 04:51:46 PM
The motion of the berg indicates that a large volume water is traveling at the top of the water column -- along the bottom of glacier. To my amateur eye, the strength of the outflow at the top of the water column seems either (1)  too great to be explained by melt-water alone (as ASLR's figure suggests is the case); or (2) the volume of melting is higher than seems to be indicated by apparent volume changes in the glacier.

I think that it is a mistake to assume that the motion of the pinned iceberg is only impacted by the out-flow of relatively fresh discharge along the base of the ice shelf, as it is probable that the keel of the iceberg is deep enough to also be impacted by the relatively warm CDW discharge shown in the first of my previous two images.  I note that this relatively warm CDW discharged from the PIIS is substantial stream (significantly larger than the meltwater stream) and is directed towards the Thwaites Glacier/Ice Shelf, where it retains sufficient heat to contribute to accelerated basal ice melt there [as I have extensively documented in numerous threads in this folder].

Edit: I also note that the relatively warm CDW discharge stream is likely also continuing to melt the basal ice of the iceberg, which could be contributing to the behavior of the iceberg.
Title: Re: PIG has calved
Post by: sidd on March 02, 2016, 08:15:19 PM
i was under the impression that sea water had no density maximum above freezing ...
Title: Re: PIG has calved
Post by: solartim27 on March 02, 2016, 08:35:07 PM
I think the motion of the pinned berg has been greatly limited by the northeast corner impacting the glacier next to it as it rotates
Title: Re: PIG has calved
Post by: AbruptSLR on March 02, 2016, 08:37:33 PM
i was under the impression that sea water had no density maximum above freezing ...

Sea water density changes with temperature, salinity and pressure and the freezing point is also a function of pressure & salinity; therefore, it is best to talk specifically about the water under the PIIS.  Perhaps the linked reference & associated images provide some insight as to the case near the iceberg:

Stanley S. Jacobs, Adrian Jenkins, Claudia F. Giulivi & Pierre Dutrieux (2011), "Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf", Nature Geoscience, Volume: 4, Pages: 519–523, doi:10.1038/ngeo1188


http://www.nature.com/ngeo/journal/v4/n8/abs/ngeo1188.html (http://www.nature.com/ngeo/journal/v4/n8/abs/ngeo1188.html)


Abstract: "In 1994, ocean measurements near Antarctica’s Pine Island Glacier showed that the ice shelf buttressing the glacier was melting rapidly. This melting was attributed to the presence of relatively warm, deep water on the Amundsen Sea continental shelf. Heat, salt and ice budgets along with ocean modelling provided steady-state calving and melting rates. Subsequent satellite observations and modelling have indicated large system imbalances, including ice-shelf thinning and more intense melting, glacier acceleration and drainage basin drawdown. Here we combine our earlier data with measurements taken in 2009 to show that the temperature and volume of deep water in Pine Island Bay have increased. Ocean transport and tracer calculations near the ice shelf reveal a rise in meltwater production by about 50% since 1994. The faster melting seems to result mainly from stronger sub-ice-shelf circulation, as thinning ice has increased the gap above an underlying submarine bank on which the glacier was formerly grounded. We conclude that the basal melting has exceeded the increase in ice inflow, leading to the formation and enlargement of an inner cavity under the ice shelf within which sea water nearly 4 °C above freezing can now more readily access the grounding zone."
Title: Re: PIG has calved
Post by: AbruptSLR on March 02, 2016, 08:39:12 PM
I think the motion of the pinned berg has been greatly limited by the northeast corner impacting the glacier next to it as it rotates

It is actually the northwest corner that has impacted the ice shelf next to it.
Title: Re: PIG has calved
Post by: steve s on March 02, 2016, 09:28:43 PM
ASLR: "... as it is probable that the keel of the iceberg is deep enough to also be impacted by the relatively warm CDW discharge shown in the first of my previous two images."

I'm confused by the first part of this comment. The berg's keel should be little deeper than the PIG's front. The second part may offer a clue. The berg's pinned, so return advective water might be a factor as it flows around the pin. There may be also orographic lifting of fluids over the eastern side of the berg, dependent on the local terrain, and about that I am ignorant. However the advective inflows must be west of the berg where the depths are greater for any of this to work out.
Title: Re: PIG has calved
Post by: AbruptSLR on March 02, 2016, 10:21:26 PM
ASLR: "... as it is probable that the keel of the iceberg is deep enough to also be impacted by the relatively warm CDW discharge shown in the first of my previous two images."

I'm confused by the first part of this comment. The berg's keel should be little deeper than the PIG's front. The second part may offer a clue. The berg's pinned, so return advective water might be a factor as it flows around the pin. There may be also orographic lifting of fluids over the eastern side of the berg, dependent on the local terrain, and about that I am ignorant. However the advective inflows must be west of the berg where the depths are greater for any of this to work out.

I base my comment on the first attached image in Reply #525, that shows that seaward of the PIIS calving face the top of the warm CDW profile bumps upward.  It is possible that this figure is out of date as the location of the calving face has changed and the amount of advected CDW varies with the location of the ABSL, which in turn varies with the ENSO and SAM phase.
Title: Re: PIG has calved
Post by: Andreas T on March 04, 2016, 12:37:13 AM


........ Fresh water's density is greatest at about 4 degrees C, so ice forms at the water's surface, where the water is at 0 degrees. Dissolved salt depresses the freezing point and increases the density, but leaves the general relationship unchanged.
.......

according to this https://nsidc.org/cryosphere/seaice/index.html (https://nsidc.org/cryosphere/seaice/index.html)
that is not correct
as salinity increases the maximum density approaches the freezing point and in sea water with salinity above 24 psu density is highest at freezing temperature
Title: Re: PIG has calved
Post by: sidd on March 04, 2016, 02:01:53 AM
So the max density temperature below the freezing point refers to supercooled salt water ?
Title: Re: PIG has calved
Post by: AbruptSLR on March 04, 2016, 02:44:51 AM
So the max density temperature below the freezing point refers to supercooled salt water ?

The density of sea water has the same pressure and temperature relationships as fresh water but, with the addition of "salt", its mass is increased (see image).
Title: Re: PIG has calved
Post by: plinius on March 04, 2016, 12:47:44 PM
You are missing out a point, ASLR, but as long as you are not an urchin, that's not lethal...
https://www.youtube.com/watch?v=lAupJzH31tc (https://www.youtube.com/watch?v=lAupJzH31tc)
Title: Re: PIG has calved
Post by: Andreas T on March 05, 2016, 06:57:58 PM
So the max density temperature below the freezing point refers to supercooled salt water ?
that is how I too interpret that graph, but I don't have other information.
 Obviously because salt forms no part of ice crystals and is frozen out as enriched brine, frozen sea water has a lower density than sea water at freezing temperature.
The graph shown by ASLR shows that salty sea water behaves like less salty sea water with added salt, but it also shows that neither has a density maximum at 4deg C.
The salinity axis in that graph just doesn't go as low as in the NSIDC graph
Title: Re: PIG has calved
Post by: Wipneus on April 09, 2016, 11:34:26 AM
Not much to report from here. The gap between the glacier and the grounded ice berg is closing. A month or so.
Title: Re: PIG has calved
Post by: oren on April 10, 2016, 11:07:52 AM
That iceberg is very stubborn  :'(
Title: Re: PIG has calved
Post by: Wipneus on April 20, 2016, 05:18:14 PM
Update: it will not take long to close the gap.
Title: Re: PIG has calved
Post by: crandles on April 20, 2016, 05:52:39 PM
What then?

A) Break off bits at end of iceberg (end that is away from PIG)?
B) Rotate iceberg further?
C) Iceberg breaks into pieces and most pieces able to float away?
D) Iceberg pushed off pinning point so can remain largely intact and float away?
E) Something else?

A and B seem most likely in the short term?
Title: Re: PIG has calved
Post by: AbruptSLR on April 20, 2016, 06:29:29 PM
What then?

A) Break off bits at end of iceberg (end that is away from PIG)?
B) Rotate iceberg further?
C) Iceberg breaks into pieces and most pieces able to float away?
D) Iceberg pushed off pinning point so can remain largely intact and float away?
E) Something else?

A and B seem most likely in the short term?

While the initial contact itself might only lead to A & B in the short-term, this contact will change the compressive stress field in the PIIS, which in my opinion will increase the probability of another major calving event in the July - August 2016 timeframe as noted in my Reply #366 (see below).  If so, another major calving event might dislodge the currently pinned iceberg.

Extract from Reply #366: "... the new major calving will occur along the crack highlighted by A-Team in Reply #357; which more or less means that I am "predicting" another major calving event in next year's July-August timeframe."
Title: Re: PIG has calved
Post by: Wipneus on April 26, 2016, 06:27:17 PM
An animation at high resolution (IW, 10m/pix) shows convincingly that the grounded ice island is rotating slightly. Remaining time for contact is about 24 days (two Sentinel 1 cycles).
Title: Re: PIG has calved
Post by: Wipneus on May 07, 2016, 12:13:51 PM
Real soon now.
Title: Re: PIG has calved
Post by: Tor Bejnar on May 07, 2016, 03:48:09 PM
There are hints of change (widening?) in the fractures across the iceberg (and ice shelf), but these might just be differences in the electromagnetic spectrum ("light" if the images had been taken with an old Earthling's camera) at image-taken times.  Whether fractures have grown or not already, I rather expect the iceberg to break into about 3 pieces when pushed seaward, given that parts of it are grounded.
Title: Re: PIG has calved
Post by: Wipneus on May 08, 2016, 12:28:55 PM
There are hints of change (widening?) in the fractures across the iceberg (and ice shelf), but these might just be differences in the electromagnetic spectrum ("light" if the images had been taken with an old Earthling's camera) at image-taken times.  Whether fractures have grown or not already, I rather expect the iceberg to break into about 3 pieces when pushed seaward, given that parts of it are grounded.

The medium resolution Sentinel images (EW extra wide, 40m/pix) make it difficult to judge such effects. You must look at the features over longer time spans and so.
Here is a high resolution (IW, Interferometric Wide, 10m/pix) animation, scaled to 40m/pix, same time of observation difference, to compare.

Title: Re: PIG has calved
Post by: solartim27 on May 15, 2016, 05:35:26 AM
Not quite there yet, but looks like you could almost jump across.  May 1 to May 13.  Gif seems to not be working, I just see the May 13 image.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160513T044346_2666_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160513T044346_2666_S_1.final.jpg)

and  S1A_EW_GRDM_1SSH_20160501T044346_1B97_S_1.final
Title: Re: PIG has calved
Post by: Wipneus on May 16, 2016, 09:02:23 AM
I'd say contact is made. Curious that this 20160513 image appeared in time on Polar View, but not in ESA's data hubs. I expect next image on 18 May, will the grounded ice island move or break?

Title: Re: PIG has calved
Post by: Shared Humanity on May 16, 2016, 03:16:59 PM
There are a lot of very visible fractures on that ice island. My guess is it will shatter.
Title: Re: PIG has calved
Post by: theoldinsane on May 16, 2016, 06:29:32 PM
Bump

What then?

A) Break off bits at end of iceberg (end that is away from PIG)?
B) Rotate iceberg further?
C) Iceberg breaks into pieces and most pieces able to float away?
D) Iceberg pushed off pinning point so can remain largely intact and float away?
E) Something else?

A and B seem most likely in the short term?

While the initial contact itself might only lead to A & B in the short-term, this contact will change the compressive stress field in the PIIS, which in my opinion will increase the probability of another major calving event in the July - August 2016 timeframe as noted in my Reply #366 (see below).  If so, another major calving event might dislodge the currently pinned iceberg.

Extract from Reply #366: "... the new major calving will occur along the crack highlighted by A-Team in Reply #357; which more or less means that I am "predicting" another major calving event in next year's July-August timeframe."

I guess that if the shelf is thicker than the island it will be another outcome compared to if the shelf and the island are of near equal thickness. Maybe anyone of the experts can comment? Anyway, it is exciting and maybe interesting for future bigger events of its kind.
Title: Re: PIG has calved
Post by: AbruptSLR on May 16, 2016, 06:43:24 PM
I guess that if the shelf is thicker than the island it will be another outcome compared to if the shelf and the island are of near equal thickness. Maybe anyone of the experts can comment? Anyway, it is exciting and maybe interesting for future bigger events of its kind.

I point-out that another major calving event will occur for the PIIS along existing crevasses; it is only a question of when, and what will trigger such a calving (as impacting the grounded iceberg is not a requirement for such a major calving event).
Title: Re: PIG has calved
Post by: theoldinsane on May 16, 2016, 07:09:45 PM
I guess that if the shelf is thicker than the island it will be another outcome compared to if the shelf and the island are of near equal thickness. Maybe anyone of the experts can comment? Anyway, it is exciting and maybe interesting for future bigger events of its kind.

I point-out that another major calving event will occur for the PIIS along existing crevasses; it is only a question of when, and what will trigger such a calving (as impacting the grounded iceberg is not a requirement for such a major calving event).

Yes, but suppose you at some point in the future have a lot of grounded islands at the same time. Will they slow down the shelf via some kind of buttress effect (negative feedback) or will they help to speed up the calving through "change the compressive stress field in the PIIS" (positive feedback). Or has it no significance?
Title: Re: PIG has calved
Post by: AbruptSLR on May 16, 2016, 07:50:09 PM
I guess that if the shelf is thicker than the island it will be another outcome compared to if the shelf and the island are of near equal thickness. Maybe anyone of the experts can comment? Anyway, it is exciting and maybe interesting for future bigger events of its kind.

I point-out that another major calving event will occur for the PIIS along existing crevasses; it is only a question of when, and what will trigger such a calving (as impacting the grounded iceberg is not a requirement for such a major calving event).

Yes, but suppose you at some point in the future have a lot of grounded islands at the same time. Will they slow down the shelf via some kind of buttress effect (negative feedback) or will they help to speed up the calving through "change the compressive stress field in the PIIS" (positive feedback). Or has it no significance?

Each case is different.  While potential buttressing from a mélange is real, it is also temporary, and the amount and influence of the buttressing is dependent on geometry and dynamics.
Title: Re: PIG has calved
Post by: theoldinsane on May 16, 2016, 08:32:38 PM
I guess that if the shelf is thicker than the island it will be another outcome compared to if the shelf and the island are of near equal thickness. Maybe anyone of the experts can comment? Anyway, it is exciting and maybe interesting for future bigger events of its kind.

I point-out that another major calving event will occur for the PIIS along existing crevasses; it is only a question of when, and what will trigger such a calving (as impacting the grounded iceberg is not a requirement for such a major calving event).

Yes, but suppose you at some point in the future have a lot of grounded islands at the same time. Will they slow down the shelf via some kind of buttress effect (negative feedback) or will they help to speed up the calving through "change the compressive stress field in the PIIS" (positive feedback). Or has it no significance?

Each case is different.  While potential buttressing from a mélange is real, it is also temporary, and the amount and influence of the buttressing is dependent on geometry and dynamics.

Ok, thanks, in a few weeks we probably have the answer in this specific event.
Title: Re: PIG has calved
Post by: oren on May 16, 2016, 09:05:41 PM
From a layman's perspective, as the glacier retreats it seems we should expect larger icebergs in the future in terms of height, therefore maybe more groundings for longer times, which might disrupt the circulation of ocean water around and under the glacier and even potentially pose as a negative feedback. Just a thought here. "in situ calving"
Title: Re: PIG has calved
Post by: AbruptSLR on May 16, 2016, 09:13:38 PM
From a layman's perspective, as the glacier retreats it seems we should expect larger icebergs in the future in terms of height, therefore maybe more groundings for longer times, which might disrupt the circulation of ocean water around and under the glacier and even potentially pose as a negative feedback. Just a thought here. "in situ calving"

Numerous marine glaciers (like Jakobshavn) have already lost their ice shelves; and during those occurrences what you are describing did not occur.  Rather, basal melting due to warm ocean water thinned the ice shelves (as did ice flow velocity), until the calving events reached the grounding line.  After that cliff failures limited the size of the associated icebergs, which also frequently roll, resulting in reduced drafts.
Title: Re: PIG has calved
Post by: oren on May 16, 2016, 11:33:29 PM
From a layman's perspective, as the glacier retreats it seems we should expect larger icebergs in the future in terms of height, therefore maybe more groundings for longer times, which might disrupt the circulation of ocean water around and under the glacier and even potentially pose as a negative feedback. Just a thought here. "in situ calving"

Numerous marine glaciers (like Jakobshavn) have already lost their ice shelves; and during those occurrences what you are describing did not occur.  Rather, basal melting due to warm ocean water thinned the ice shelves (as did ice flow velocity), until the calving events reached the grounding line.  After that cliff failures limited the size of the associated icebergs, which also frequently roll, resulting in reduced drafts.

Thanks ASLR for your excellent answer. Now things are clearer.
Title: Re: PIG has calved
Post by: solartim27 on May 18, 2016, 08:06:43 AM
Not quite there yet (or so it looks to me)
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160516T033006_D9EB_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160516T033006_D9EB_S_1.final.jpg)
Title: Re: PIG has calved
Post by: Wipneus on May 18, 2016, 08:29:55 AM
Not quite there yet (or so it looks to me)


You are right, the ice island has not moved a bit.
Title: Re: PIG has calved
Post by: Wipneus on May 19, 2016, 09:13:22 AM
But now it did.
Title: Re: PIG has calved
Post by: Wipneus on May 20, 2016, 06:23:10 PM
The higher resolution IW images are better, even when scaled from 10 m/pix to 30 m/pix.
Title: Re: PIG has calved
Post by: AbruptSLR on May 20, 2016, 07:02:30 PM
The higher resolution IW images are better, even when scaled from 10 m/pix to 30 m/pix.

It is possible that the change in the stress field in the PIIS associate with this contact contributed to the calving event shown in the "notch" area of the PIIS.
Title: Re: PIG has calved
Post by: Wipneus on May 22, 2016, 11:04:46 AM
Another animation of the collision. From this and the previous, I think the ice island is being deformed (by some process). The top of the island (that meets the glacier front) can be seen moving with the glacier and sideways. The opposite tip does not move so much, not fully explained by a rotation of the island.
The Red/Green image shows how each side from the island has moved between the Sentinel 1A visits and shows the same: the island's top moves more than the rest of the island.
All images scaled to 30m/pix.
Title: Re: PIG has calved
Post by: Tor Bejnar on May 22, 2016, 03:07:03 PM
In the later of the two images, I definitely see evidence of a 'new' crack going from near the upper right point of the iceberg (ice island?) toward the uppermost crack on the left side.  I see what I think is evidence of that uppermost left side crack extending further into the berg.  (I do not see the two cracks actually connecting.)  Besides this tiny bit of deformation, I imagine the entire iceberg is pivoting on the most significant (of, I presume multiple) grounding point that (estimating from the rotation indicated by the red/green image and looking at the 2-image movie) is fairly close to (but not at) the lower left point of the iceberg.
Title: Re: PIG has calved
Post by: Wipneus on May 30, 2016, 03:10:30 PM
Latest Sentinel image is from 2016-05-30 and I compare it with one cycle ago 18th May.
I have rotated the images 0.3o and shifted to align the images of the ice island as good as I could in the Gimp. On this medium resolution (GRDM, 40m/pix) there is no unambiguous deforming visible: the island is moving as a whole.
Title: Re: PIG has calved
Post by: Wipneus on May 31, 2016, 06:47:00 PM
Same as yesterday, but now with two higher resolution images (IW, or 10 m/pix, here shown at 20 m/pix).
Somehow I had to rotate the images 0.55o to align them, nearly twice as yesterday.

Anyway, no unambiguous deformation of the ice island visible.

(needs a click to animate)
Title: Re: PIG has calved
Post by: AbruptSLR on May 31, 2016, 07:25:41 PM

Anyway, no unambiguous deformation of the ice island visible.


While there is no unambiguous deformations of the grounded iceberg (ice island); I note that there is clearly a new shear-tension crack in the notch area; which supports my prior projection that we may well witness a new major calving event for the PIIS in the late July to August, 2016 timeframe.
Title: Re: PIG has calved
Post by: Wipneus on June 03, 2016, 08:51:39 AM
Here is an animation of a detail of the ice island (hi-res IW, 10m/pix sclaed to 5m/pix) that may show new cracks developing. It is all very vague and perhaps just noise, have a look.
Title: Re: PIG has calved
Post by: Tor Bejnar on June 03, 2016, 05:28:36 PM
Thanks.  I've been 'seeing things' (cracks, I contend) on the low-res image pairs, some of which match your hi-res image pairs (but they don't all match).  Time will tell which are phantom and which are physical.
Title: Re: PIG has calved
Post by: AbruptSLR on June 03, 2016, 06:44:35 PM
Thanks.  I've been 'seeing things' (cracks, I contend) on the low-res image pairs, some of which match your hi-res image pairs (but they don't all match).  Time will tell which are phantom and which are physical.

I note that it is likely that when the next major calving event happens for the PIIS (possibly in the late July to August timeframe) that the newly calved icebergs may either refloat the grounded/pinned "ice island", or alternately cause it to fracture into smaller free-floating icebergs.
Title: Re: PIG has calved
Post by: Wipneus on June 08, 2016, 08:22:00 AM
The low res (EW or 40m/px) image of 6 June hints at something similar in the same spot.
Title: Re: PIG has calved
Post by: solartim27 on June 12, 2016, 08:59:54 PM
A large chunk breaks off the island.  Looks like break up will come pretty soon.
Dates are May 30 and Jun 11
S1A_EW_GRDM_1SSH_20160611T045153_EC09_S_1.final
S1A_EW_GRDM_1SSH_20160530T045153_044B_S_1.final
Title: Re: PIG has calved
Post by: AbruptSLR on June 12, 2016, 11:00:23 PM
A large chunk breaks off the island.  Looks like break up will come pretty soon.
Dates are May 30 and Jun 11

Great catch.  However, it is possible/likely that this calving event from the iceberg was associated with rotational restraint offered by the chunk that broke-off.  Now that the rotational restraint is no longer active, perhaps the pinned iceberg is more stable (from fracturing) than before this event. 

In any event, it will be interesting to see what happens next.
Title: Re: PIG has calved
Post by: Wipneus on June 13, 2016, 09:10:11 AM
The pressure on the pointed tip of the ice island seems to have done it.

In the same time frame another calving on the other side of the glacier.

Animation from hi-res (IW) images, scaled to 70m/pix for size.
Title: Re: PIG has calved
Post by: AbruptSLR on June 13, 2016, 10:45:05 AM

In the same time frame another calving on the other side of the glacier.


Just for the record, the "... calving on the other side of the glacier" is actually a calving from what MacGregor et al 2013 calls the Southwest (SW) Tributary Glacier (which flows out of the Thwaites Basin) as in the first attached image, as well as in the second attached image from Ng 2015 (with a hat-tip to A-Team).
Title: Re: PIG has calved
Post by: notjonathon on June 24, 2016, 01:57:01 AM
ALSR--

It looks like the moving front of the glacier is pivoting the ice island around. That should put some torsional pressure on weaker sections of the island and encourage further breakup.

Also, do the new calving fronts (the cracks further up the ice) actually calve when they reach the present front point, or is there significant retreat going on? I should know, but trying to follow everything that's going on in both the Arctic and Antarctic taxes my memory.
Title: Re: PIG has calved
Post by: AbruptSLR on June 24, 2016, 05:06:47 AM
notjonathon,

The calving front is progressively retreating upstream & it seems plausible to me that crevasse upstream of calving front might rupture sometime in the late July to mid-August 2016 timeframe.

Best,
ASLR
Title: Re: PIG has calved
Post by: oren on June 24, 2016, 08:31:16 AM
Wow. Two developments at the same time in this slow-moving monster.
The ice island is doomed one way or another, but the tributary glacier supplies part of the buttressing of the PIG. Calving there could speed up calving of PIG itself.
Title: Re: PIG has calved
Post by: solartim27 on June 30, 2016, 11:31:51 PM
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11
S1A_EW_GRDM_1SSH_20160630T044349_949F_S_1.final.jpg
S1A_EW_GRDM_1SSH_20160611T045153_EC09_S_1.final.jpg
Title: Re: PIG has calved
Post by: AbruptSLR on June 30, 2016, 11:38:31 PM
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11

It might still be pinned against translation & only free to rotate about the pinning point.
Title: Re: PIG has calved
Post by: crandles on July 01, 2016, 01:54:41 AM
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11

It might still be pinned against translation & only free to rotate about the pinning point.

Suggests a single pinning point else it wouldn't have rotated so far?

Rotation centre doesn't seem close to any edge. Might break up but if it doesn't, it would seem PIG has to advance a long way to push it off its pinning point.
Title: Re: PIG has calved
Post by: magnamentis on July 01, 2016, 11:43:40 AM
Looks more like a rotation event than breaking free.  Jun 30 vs Jun 11

It might still be pinned against translation & only free to rotate about the pinning point.

having fun reading this what i just wanted to post which is great, i like common sense if it makes sense LOL
Title: Re: PIG has calved
Post by: Adam Ash on July 01, 2016, 02:33:16 PM
Seems from those two images that the rotation is about a point in from the edge. 

The small bay at the top of the image and the grid line stay put during the switch between images, but you can see that the calving face advanced some towards the rotated slab.  So it may not be long before it gets a nudge from the glacier which may dislodge it some.

First image is or rotation, second shows my identification of points, normals and arcs which derive a fair idea of roughly where the centre of rotation is (was).
Title: Re: PIG has calved
Post by: Tor Bejnar on July 01, 2016, 04:33:28 PM
I think it is possible that the iceberg (ice island?) is slipping on the single pivot point, preventing Adam Ash's arcs from defining a single point.  A third day's addition to the image layers would expose this possibility.  (I wish I had the software to do what Adam did   :'()
Title: Re: PIG has calved
Post by: Adam Ash on July 02, 2016, 10:40:01 AM
Hi Tor!  My diagram shows the 'berg is rotating about the single pivot point defined by the small magenta circle with a cross in it, among the normal rays.  All the arcs are from that centre point.

A single pivot point is likely to be under enormous strain and wont last long, I suspect.

Software used is Gimp (for the graphics and GIF) and BricsCad for the line work, and the W10 Snipper tool.
Title: Re: PIG has calved
Post by: solartim27 on July 04, 2016, 06:00:18 PM
No apparent changes, looks like we need to wait for the next contact from the glacier.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160703T033009_71B9_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160703T033009_71B9_S_1.final.jpg)
Title: Re: PIG has calved
Post by: Adam Ash on July 12, 2016, 09:19:52 AM
This Modis mosaic dated 20160711 seems to suggest that the berg has swung back in against the coast.  The 4km resolution is not clear, but the berg should show and there is no sign of the berg in its previous location.

Other nearby features shown to help you locate (the Molar and the Bite).
Title: Re: PIG has calved
Post by: solartim27 on July 12, 2016, 05:08:56 PM
This Modis mosaic dated 20160711
Where is this from?  It's winter there. 
Edit:  Never mind, found it on the Polar view Mosaics tab.  Since Worldview has it as dark, I always figured that was dark too.
Edit:  Matches the worldview image for 20160405.
Title: Re: PIG has calved
Post by: Adam Ash on July 13, 2016, 09:19:32 AM
Thanks for checking Solar..  I assumed Modis was radar so immune to day/night.  You could be right.

Will wait for the next pass of S1.
Title: Re: PIG has calved
Post by: solartim27 on July 17, 2016, 09:02:02 PM
Nothing exciting, some rotation and advance.  6/30 to 7/17.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20160630T044349_949F_S_1.final.jpg
Title: Re: PIG has calved
Post by: solartim27 on July 26, 2016, 06:06:28 AM
Same changes as last weeks post.  Jul 17 to Jul 24.
http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160724T044353_54D3_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160724T044353_54D3_S_1.final.jpg)

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160717T045158_6AF6_S_1.final.jpg)
Title: Re: PIG has calved
Post by: Wipneus on July 31, 2016, 05:23:44 PM
Sequence of Sentinel 1 images scaled to 30m/pix to capture both the ice island and the crack. The island seems to move freely and will probably be parallel with the calving front before significant pressure will be applied. I estimate the gap at least 60 pixels or 1.8 km wide, at an average speed of 10m/day it will take us into 2017 when that happens. In that time frame something else may break of course.
Title: Re: PIG has calved
Post by: Adam Ash on August 03, 2016, 09:48:54 AM
The centre of rotation has not moved far where it was a month ago.  First image 1 July, second image 31 July 2016. 

(Apologies for not rotating the images to the same orientation)
Title: Re: PIG has calved
Post by: steve s on August 03, 2016, 03:34:13 PM
Looks to me as though a crevasse is extending toward the point of rotation and another is extending in a pattern that would separate the pinning point from the rest of the berg. Both crevasses are either racing thinning to free the berg by breaking it up, or they are products of thinning.

Any guesses as to when the berg will drift free?
Title: Re: PIG has calved
Post by: AbruptSLR on August 03, 2016, 04:53:37 PM
Looks to me as though a crevasse is extending toward the point of rotation and another is extending in a pattern that would separate the pinning point from the rest of the berg. Both crevasses are either racing thinning to free the berg by breaking it up, or they are products of thinning.

Any guesses as to when the berg will drift free?

I believe that the crevasses that we see are left-over from shear stresses while the ice shelf was shearing against the adjacent landmass/shoring.  Also, I believe that the berg will drift free when the PIIS calves again sometime between next week and the end of November 2016.
Title: Re: PIG has calved
Post by: Tor Bejnar on August 03, 2016, 06:21:44 PM
Looks to me as though a crevasse is extending toward the point of rotation and another is extending in a pattern that would separate the pinning point from the rest of the berg.
...
I saw those also, but didn't write anything because I've seen what I thought were extending cracks that didn't amount to anything, and the apparent extensions may have been due to changing angles (the ice island is rotating) rather than growing cracks.  (Or growing cracks could stop growing...).

If these are real, the island could break 'any day' (what do I know), but would likely split if hit by a new ice island or berg or tongue.
Title: Re: PIG has calved
Post by: solartim27 on August 12, 2016, 06:36:05 AM
More rotation and advance.  The crack in the glacier seems to extend quite a bit, but it could just be differences in the view.  Jul 24 - Aug 10
S1A_EW_GRDM_1SSH_20160810T045157_3C95_S_1.final.jpg
S1A_EW_GRDM_1SSH_20160724T044353_54D3_S_1.final.jpg
Title: Re: PIG has calved
Post by: Wipneus on August 12, 2016, 08:48:17 AM
More rotation and advance.

... and the ice island lost a shard ("bottom" left corner).
Title: Re: PIG has calved
Post by: solartim27 on August 23, 2016, 03:09:59 PM
Ice island has spun 'downstream', but it doesn't look free floating yet.  The next impact will send it on its way, if it doesn't break off before.
Title: Re: PIG has calved
Post by: solartim27 on August 28, 2016, 05:45:22 AM
What a tease.
Title: Re: PIG has calved
Post by: nukefix on August 28, 2016, 04:09:23 PM
What a tease.
Use radar :D
Title: Re: PIG has calved
Post by: Wipneus on August 29, 2016, 04:04:11 PM
Turned back (or 270 degrees forward, who knows).
Title: Re: PIG has calved
Post by: solartim27 on September 03, 2016, 04:16:07 AM
Ice island has broken free.  Aqua 9/2
Title: Re: PIG has calved
Post by: solartim27 on September 13, 2016, 10:23:18 PM
The calving front is progressively retreating upstream & it seems plausible to me that crevasse upstream of calving front might rupture sometime in the late July to mid-August 2016 timeframe.
This did not come to pass, but I think it's going to soon.  Gif dates are 8/31 and 9/12.  When zoomed in, it looks to me like the crack is propagating diagonally down to the coast towards the bottom right corner.  Ice island is just off screen in the later shot.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160912T042739_E260_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160912T042739_E260_S_1.final.jpg)


http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160831T042738_E6CA_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20160831T042738_E6CA_S_1.final.jpg)
Title: Re: PIG has calved
Post by: AbruptSLR on September 14, 2016, 12:03:32 AM
The calving front is progressively retreating upstream & it seems plausible to me that crevasse upstream of calving front might rupture sometime in the late July to mid-August 2016 timeframe.
This did not come to pass, but I think it's going to soon.  Gif dates are 8/31 and 9/12.  When zoomed in, it looks to me like the crack is propagating diagonally down to the coast towards the bottom right corner.  Ice island is just off screen in the later shot.

In Reply #452, I state: "As a side-note I speculate that the next major rift will form a failure mechanism by about July 2016 with a major calving following sometime between July 2016 and November 2016, depending on boundary conditions and on whether fast sea ice is present."  So I still have a chance of being partially correct (or at least not totally wrong) ;D.
Title: Re: PIG has calved
Post by: oren on September 14, 2016, 12:23:45 AM
Out of curiosity, I wanted to find out how long the grounded iceberg stayed before it finally went away.
Amazingly enough, it was more than a year!
It calved at the end of July 2015 with most of the calved ice disappearing away. The grounded part broke up mid-August with another piece floating away, and ever since then our PIG-headed iceberg just kept holding on.
Would it be fair to speculate that the glacier is partially grounded at this area? If a calved iceberg can stay grounded for so long, it must mean it was grounded before the calving as well.
To entertain more idle speculation, would the calving and subsequent removal of this iceberg reduce the buttressing of the PIG?
Title: Re: PIG has calved
Post by: DoomInTheUK on September 14, 2016, 12:41:29 PM
It could imply the the iceberg was stuck on the grounding line and the calving front has now moved back off the grounding line. Not a nice thought.
Title: Re: PIG has calved
Post by: solartim27 on September 16, 2016, 05:37:55 PM
It could imply the the iceberg was stuck on the grounding line and the calving front has now moved back off the grounding line. Not a nice thought.
The berg was just stuck on a pinnacle, there were quite a few posts on the grounding line retreat back on pages 8 - 9, and on some other threads, it is well back from the front of the ice shelf.  I have not seen anything recently, but I expect the El Nino did cause it to retreat quite a bit. It was interesting to review the discussions of the retrograde beds in the area.
Here is the first clear image of the year, from Terra.  looking back at the last calving, the crack then was much more defined before it went.  Maybe the snow hills on top were fooling me into thinking I saw crack propagation.
Title: Re: PIG has calved
Post by: Adam Ash on September 20, 2016, 10:09:26 AM
PIG's TwiddleBerg seems to have gone west.  It was about 10 km long (roughly), and the only likely candidate for it is among the broken ice at the lower of this view, about 50 km away from where it started.  Not certain, tho.
Title: Re: PIG has calved
Post by: Wipneus on September 28, 2016, 07:09:30 PM
Meanwhile the glacier is advancing and the crack widening. Here is a detail of the right hand side where widening and lengthening in the 60 day span is clear. Both images in the animation are aligned on the crack, noting the displacement the glacier was moving 11.6 m/day.
Title: Re: PIG has calved
Post by: Wipneus on October 08, 2016, 05:21:40 PM
First usable Landsat image of the summer season is in. Still cloudy but the crack is visible. Here is an animation made with the last available image of the previous season showing the visible crack has both widened and lengthened by about 50%.

Must click to start as the crack does not fit anymore in the standard 700x700 box.
Title: Re: PIG has calved
Post by: oren on October 08, 2016, 07:12:49 PM
By layman analysis, looks like it's going to calve this summer. If it does, it will be another retreat of the calving front.
Title: Re: PIG has calved
Post by: prokaryotes on October 18, 2016, 11:50:08 PM
Did something break? Is this area part of PIG?

Link https://worldview.earthdata.nasa.gov/?p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2016-10-16&v=-1729024,-485504,-1483264,-355968 (https://worldview.earthdata.nasa.gov/?p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2016-10-16&v=-1729024,-485504,-1483264,-355968)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FSMPUol0.jpg&hash=b5c99630598756bb0e7be7f0e2fa7854)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2Faa6keCU.jpg&hash=da07a9e9212af35f259f983bdc6fa357)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FRnAMmxi.jpg&hash=2e257e41fd016f67a5ee94ba1bc91147)


Title: Re: PIG has calved
Post by: AbruptSLR on October 19, 2016, 12:23:42 AM
Did something break? Is this area part of PIG?

The image shows sea ice breaking away from the Thwaites Ice Shelf; so the image does not indicate any significant iceberg calving.

Best,
Dale
Title: Re: PIG has calved
Post by: prokaryotes on October 19, 2016, 01:05:17 AM
The image shows sea ice breaking away from the Thwaites Ice Shelf; so the image does not indicate any significant iceberg calving.

Best,
Dale
For clarification, the topic is about large calving event, the iceberg is referred to as B31, first cracked then stalled, then finally begun moving around 2013
http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=82392 (http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=82392)

Then drifted along 2014
http://earthsky.org/earth/nasa-is-tracking-a-gargantuan-iceberg-escaped-from-antarctica (http://earthsky.org/earth/nasa-is-tracking-a-gargantuan-iceberg-escaped-from-antarctica)


Correct? Thanks.
Title: Re: PIG has calved
Post by: oren on October 19, 2016, 01:16:55 AM
For clarification, the topic is about large calving event, the iceberg is referred to as B31, first cracked then stalled, then finally begun moving around 2013
...
Correct? Thanks.
The topic has since moved on to discuss other PIG calvings as they happen.
Title: Re: PIG has calved
Post by: prokaryotes on October 19, 2016, 01:26:07 AM
The topic has since moved on to discuss other PIG calvings as they happen.
Ok, but the original iceberg, is that now the one known as B31?
http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=82392 (http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=82392)

I am asking, because i am currently editing a video (the 3rd one here https://svs.gsfc.nasa.gov/11135 (https://svs.gsfc.nasa.gov/11135) ), and want to update the information. Thanks

Title: Re: PIG has calved
Post by: AbruptSLR on October 19, 2016, 01:13:55 PM
For current information about the locations of large Antarctic icebergs, see:

http://www.scp.byu.edu/current_icebergs.html (http://www.scp.byu.edu/current_icebergs.html)
Title: Re: PIG has calved
Post by: jai mitchell on October 26, 2016, 06:23:37 PM
Update of Rignot's work on West Antarctic Pasin

video presentation 2 minutes

https://www.youtube.com/watch?v=YQMtb1Pd07E (https://www.youtube.com/watch?v=YQMtb1Pd07E)
Title: Re: PIG has calved
Post by: Wipneus on November 01, 2016, 07:07:03 PM
First Sentinel 2 image is available and is brilliant! It is part of what ESA describes as a:
special acquisition campaign of Antarctica between 17th and
27th October (one repeat cycle), taking benefit of the margin currently offered
by the reduced illumination at Northern latitudes.

Hopefully Antarctica will share some more of those benefits while the illumination in the NH stays low.

Attached is a 20m/pix image covering the whole crack (about 150m wide in the middle).The second image covers the southern tip of the crack showing some beautiful details at 5m/pix (oversampled from native 10m/pix).
Title: Re: PIG has calved
Post by: solartim27 on November 07, 2016, 05:38:33 PM
Here's a nice shot from https://twitter.com/NASA_ICE (https://twitter.com/NASA_ICE) 
Title: Re: PIG has calved
Post by: AbruptSLR on December 01, 2016, 12:19:43 AM
The calving front is progressively retreating upstream & it seems plausible to me that crevasse upstream of calving front might rupture sometime in the late July to mid-August 2016 timeframe.
This did not come to pass, but I think it's going to soon.  Gif dates are 8/31 and 9/12.  When zoomed in, it looks to me like the crack is propagating diagonally down to the coast towards the bottom right corner.  Ice island is just off screen in the later shot.

In Reply #452, I state: "As a side-note I speculate that the next major rift will form a failure mechanism by about July 2016 with a major calving following sometime between July 2016 and November 2016, depending on boundary conditions and on whether fast sea ice is present."  So I still have a chance of being partially correct (or at least not totally wrong) ;D.

As it is Nov 30th and no major calving occurred for the PIIS, it is reasonable to conclude that my forecast was too bullish.
Title: Re: PIG has calved
Post by: CraigsIsland on December 01, 2016, 12:43:58 AM
The calving front is progressively retreating upstream & it seems plausible to me that crevasse upstream of calving front might rupture sometime in the late July to mid-August 2016 timeframe.
This did not come to pass, but I think it's going to soon.  Gif dates are 8/31 and 9/12.  When zoomed in, it looks to me like the crack is propagating diagonally down to the coast towards the bottom right corner.  Ice island is just off screen in the later shot.

In Reply #452, I state: "As a side-note I speculate that the next major rift will form a failure mechanism by about July 2016 with a major calving following sometime between July 2016 and November 2016, depending on boundary conditions and on whether fast sea ice is present."  So I still have a chance of being partially correct (or at least not totally wrong) ;D.

As it is Nov 30th and no major calving occurred for the PIIS, it is reasonable to conclude that my forecast was too bullish.

there's a few hours left (I think) for the 30th. maybe it happens tomorrow? lol. I think your estimation was reasonable and we'll see when/how/if that estimation can help us to understand a bit better about later possible calving.
Title: Re: PIG has calved
Post by: Tealight on December 01, 2016, 12:53:32 AM
I've taken some dimensions with SNAP. If the rift continues in a straight line the calved iceberg will be roughly 8.8km x 39km. The total area is 326km2. This is in a completely different league than anything from Greenland.
Title: Re: PIG has calved
Post by: Wipneus on December 05, 2016, 05:21:00 PM
No need to explain, I suppose. Sentinel 2 images scaled to 5m/pix, 6 weeks apart.
Title: Re: PIG has calved
Post by: oren on December 05, 2016, 05:55:52 PM
No need to explain, I suppose. Sentinel 2 images scaled to 5m/pix, 6 weeks apart.
Wow.
Title: Re: PIG has calved
Post by: Greenbelt on December 06, 2016, 10:45:54 PM
No need to explain, I suppose. Sentinel 2 images scaled to 5m/pix, 6 weeks apart.

In this image comparison, the features in the "upper" part (above the crack) look to be moving "up and left" while those in the "lower part" look to be moving down and left?  Thus the cracking, I suppose.
Title: Re: PIG has calved
Post by: solartim27 on December 10, 2016, 08:45:10 PM
This series is also about 6 weeks apart, Oct 28 to Dec 8.  Different satellites, so the pairing may not be ideal, sure looks like it gets a lot longer.

http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20161209T044310_189A_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20161209T044310_189A_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20161028T044353_32E1_S_1.final.jpg
Title: Re: PIG has calved
Post by: Tealight on December 11, 2016, 01:58:35 PM
Last year in November A-Team and Nukefix posted a few images of fault lines on Pine Island Glacier spanning across several square kilometers. The area begins approx. 125km upstream from the calving front. Their posts start at #454.

Now I looked the areas again with Sentinels 2A, 10m resolution in RGB colour. This gives us a new perspective compared to Landsats 15m grey scale or even lower resolution radar.

Most noticable is the deep blue inside those cracks. I'm not sure if its liquid water or simply a shadow on blue ice. Some cracks on the third image show light blue areas without a shadow. The question with liquid water is where the energy comes from to melt ice. Maybe geothermal heat propagates from the bedrock all they way through the glacier to the surface. Hot steam would surely be capable of melting the surface of these edges. Does anyone has a different idea?

Title: Re: PIG has calved
Post by: steve s on December 11, 2016, 09:42:33 PM
Tealight,

The dark areas look like places where snow bridges did not form or collapsed. I think the curved crevasses in the third image, with the obvious wind-formed ridges of snow crossing some crevasses, may show the main bridging process.
Title: Re: PIG has calved
Post by: solartim27 on December 15, 2016, 06:42:13 PM
Here is a visual worldview gif from Nov 8 to Dec 13, Aqua band.  Minor calvings in the notches on either side of PIG, and along the front.  I've left it full size, so click to animate.  (Bummer that worldview seems to be down with the full moon tides)

I think there is some interesting activity along the SW Tributary boundary at the bottom right of the image, previously discussed in this thread:
This will cause the buttressing on the SW Tributary Glacier to be reduced, which will help to trigger the acceleration of ice velocities for Thwaites:
Title: Re: PIG has calved
Post by: solartim27 on December 17, 2016, 08:39:01 PM
Here's a Sentinel gif from Dec 3 to 17.  Looks to me like both PIG and the Tributary are going to go soon.  One image small, and one left full size.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161217T042738_2F36_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20161217T042738_2F36_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20161203T044353_2FFE_S_1.final.jpeg
Title: Re: PIG has calved
Post by: solartim27 on December 17, 2016, 09:10:14 PM
Here's a zoomed in gif of the boundary area from above.  It's full size to see the crack development.  (Clicking didn't work for me, but it did animate when I selected "Open in a new tab".  Of course you could just zoom in on that area in the full gif in the post above.)
Title: Re: PIG has calved
Post by: Wipneus on December 24, 2016, 12:14:00 PM
The crack is widening fast.  It can not be long now.
Title: Re: PIG has calved
Post by: Wipneus on December 24, 2016, 12:26:18 PM
Another one, magnified 4 times to 2.5 m/pix, shows the western tip of the crack.
Title: Re: PIG has calved
Post by: Hans on December 25, 2016, 06:16:59 PM
Not knowing exactly where PIG was, I started google maps. I was surprised by the details of some photo's. Not the most recent ones, of course, But nevertheless worth a visit
https://www.google.nl/maps/@-75.0761623,-101.4182596,3682m/data=!3m1!1e3 (https://www.google.nl/maps/@-75.0761623,-101.4182596,3682m/data=!3m1!1e3)
Zooming in and wandering around gives some nice details.
Title: Re: PIG has calved
Post by: oren on December 26, 2016, 12:19:52 AM
Thanks Hans, I never realized Google might have this level of detail. It's funny how the PIG crack is highly detailed in one tile but non-existent in the next one.
Title: Re: PIG has calved
Post by: bbr2314 on December 26, 2016, 03:27:20 AM
Looking at EOSDIS it seems as though the entire front is now moving forward noticeably, perhaps crack has greatly expanded?
Title: Re: PIG has calved
Post by: iwantatr8 on December 27, 2016, 07:57:41 AM
Looking at the latest sentinel here
http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20161226T045115_30DF_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20161226T045115_30DF_S_1.final.jpg)
(Warning large photo)
There appears to be a new crack starting 1/3 of the way back from the face to the larger crack we've been following.
A race now I feel, between this and the existing crack as to which will be the first to calve.
I'm not sure that we will see anything this year given the few days left but early January seems likely.

Sorry for the lack of an image, posting from a mobile.
Title: Re: PIG has calved
Post by: Iceismylife on December 27, 2016, 05:39:01 PM
Thanks Hans, I never realized Google might have this level of detail. It's funny how the PIG crack is highly detailed in one tile but non-existent in the next one.
Put a pin in where it isn't and it will trigger updating.  (on occasion)
Title: Re: PIG has calved
Post by: Wipneus on January 07, 2017, 10:17:42 AM
The calving-in-progress continues...
Title: Re: PIG has calved
Post by: frankendoodle on January 07, 2017, 10:26:23 PM
When the glacier fully calves the iceberg will be about the size of the island of Grenada in the Caribbean.
Title: Re: PIG has calved
Post by: Wipneus on January 25, 2017, 09:09:42 AM
Two Landsat 8 images, 16 days apart (so taken from identical satellite positions), suggest that the near future big calving is moving and rotating relative from the main glacier.
Title: Re: PIG has calved
Post by: solartim27 on January 27, 2017, 12:22:28 AM
Some action at the front, small calving.  Terra images from 25 and 26.  Aqua is too
 cloudy.
Title: Re: PIG has calved
Post by: Wipneus on January 27, 2017, 10:41:47 AM
It is big enough, could be the start.

(click for the big picture)
Title: Re: PIG has calved
Post by: Wipneus on January 27, 2017, 11:17:31 AM
Detail shows a fine crack where the next calving will go. How far will this crack extend?
Title: Re: PIG has calved
Post by: oren on January 28, 2017, 08:39:05 AM
Dumb question time. How is PIG related to the long Larsen C crack shown here:
It's unrelated: PIG is a glacier with an ice shelf at the end, Larsen C is an ice shelf with several glaciers behind it. Larsen C is east of the Antarctic Peninsula, PIG is in West Antarctica. PIG calving period is years, Larsen C is decades. Calving size is smaller in PIG. PIG is much more important as it drains a large part of West Antarctica. Hope I helped a bit, but perhaps you can clarify what you meant: Geographically? Same processes? etc.
Title: Re: PIG has calved
Post by: Hans on January 28, 2017, 10:25:27 AM
Dumb question time. How is PIG related to the long Larsen C crack shown here:
Hi Susan, I think the crack in LarsenC is around 150 km long now.
The full width of PIG is around 40 km
The length of the fraction that cracked of in the images of 26 January is.. well.. just a fraction of it. ;)
Title: Re: PIG has calved
Post by: Susan Anderson on January 28, 2017, 10:42:28 PM
Thanks oren and Hans, that's exactly what I needed and I was way off topic. I'm taking a closer look at the riches on the forum, a treasure trove (!), now have a much better idea of the geography and effects, and found a paper map. Time for some study! Meanwhile, it is all fascinating and bloody dangerous. My question almost defines dumb, and I see there's a place for that too! ;)
Title: Re: PIG has calved
Post by: LRC1962 on January 29, 2017, 12:48:46 AM
Another big difference is how. Larsen |C started at an ocean point and is working its way across to another ocean point. much like tearing a piece of paper. The PIG is a very different story.
West Antarctic ice shelf breaking up from the inside out (https://phys.org/news/2016-11-west-antarctic-ice-shelf.html).
Rift in Pine Island Glacier ice shelf, West Antarctica, photographed from the air during a NASA Operation IceBridge survey flight on Nov. 4, 2016. This rift is the second to form in the center of the ice shelf in the past three years. The first resulted in an iceberg that broke off in 2015.
In the images, they saw evidence that a rift formed at the very base of the ice shelf nearly 20 miles inland in 2013. The rift propagated upward over two years, until it broke through the ice surface and set the iceberg adrift over 12 days in late July and early August 2015.
This article is telling about what happened in 2015, but based on caption of first photo which I quote, it seems to be the same process involved for this event.
Title: Re: PIG has calved
Post by: Susan Anderson on January 30, 2017, 06:53:35 AM
I've removed the big Larsen C graphic and my query as it was so glaringly off topic and I don't think it was needed for the good answers y'all provided. Thanks everyone for the work here and elsewhere, an excellent range of visual and information aids.
Title: Re: PIG has calved
Post by: Wipneus on January 31, 2017, 09:00:03 AM
Five days later, no further calving yet.
Title: Re: PIG has calved
Post by: solartim27 on February 04, 2017, 05:22:21 PM
Here is a gif from Jan 5 (?) to Feb 1 of the rift in the SW Tributary glacier next to PIG from
http://apps.sentinel-hub.com/sentinel-playground/#lat=-75.08856670583675/lng=-101.36260986328125/zoom=11/preset=CUSTOM/layers=B05,B03,B01/maxcc=8/gain=0.4/time=2015-01-01|2017-02-01/cloudCorrection=none/colCor=/evalscript= (http://apps.sentinel-hub.com/sentinel-playground/#lat=-75.08856670583675/lng=-101.36260986328125/zoom=11/preset=CUSTOM/layers=B05,B03,B01/maxcc=8/gain=0.4/time=2015-01-01|2017-02-01/cloudCorrection=none/colCor=/evalscript=)
The main crack in PIG was not updated between images so I cropped it off.  I'm not certain of the dates for the first image, which you can tell is a mosaic of two separate images.
Title: Re: PIG has calved
Post by: AbruptSLR on February 04, 2017, 06:10:52 PM
Here is a gif from Jan 5 (?) to Feb 1 of the rift in the SW Tributary glacier next to PIG from

Thanks for this nice gif sequence highlighting the opening of the rift in the SW Tributary ice shelf.  The attached image shows a Sentinel 2 image from Feb 2 2017 of both the PIIS and the SW Tributary ice shelf, to which I have added a segmented yellow line indicating the approximate location of where I am concerned that the next upstream crack will occur in the PIIS as the rift in the SW Tributary ice shelf continues to open.  If I am correct, the opening of such an upstream crack would cause a major calving event along the location of the current crack in the PIIS.
Title: Re: PIG has calved
Post by: Wipneus on February 15, 2017, 08:47:54 AM
The recent calving is the subject of Nasa's Earth Observatory Image of the Day

Glacial “Aftershock” Spawns Antarctic Iceberg (http://earthobservatory.nasa.gov/IOTD/view.php?id=89638)

The discussion mentions: ‘rapid fire’ calving
Title: Re: PIG has calved
Post by: Jim Hunt on February 15, 2017, 01:10:38 PM
The recent calving is the subject of Nasa's Earth Observatory Image of the Day

In addition NASA's first reference is to this very forum.

Well done SolarTim, Wipneus et al.!
Title: Re: PIG has calved
Post by: oren on February 15, 2017, 02:16:01 PM
I actually missed the ASIF reference at first. Nice!
Title: Re: PIG has calved
Post by: DrTskoul on February 15, 2017, 03:23:31 PM
Testament to the superb scientific discovery and analysis work done at AIF!!
Title: Re: PIG has calved
Post by: solartim27 on April 17, 2017, 09:58:51 PM
Thinking more about the lateral compression, it seems that there is a compression from the opposite side, a bit further down. This pushed the calving face to the river right, after passing Evans Knoll.

I suspect, but can't prove, that this deformation force increases the backpressure on the rest of the glacier, as it forces the visible bend to the river right.

I suspect that this deformation was part of the reason the calving broke off the way it did (first the river right, the the river left last, as it was in compression for the longest). I think this may be a protective factor, decreasing the chance of a large calving soon. I hope.

I worry about the rate of decline once the calving front passes those lateral pinning points.  That's when it'll really start flying. :(

A is the compression force due to Evans Knoll, B is the one on the opposite, causing the flexion around Evans Knoll.
I was surprised that PIG didn't go this summer, but it still looks like it can go at any time, as we are seeing increasing amounts of minor calving at the notches to either side of PIG. 

I believe the compression from the SW Trib described above is keeping it penned in.  There is a good image on that post, worth going back to review.
Click to animate and zoom in for a closer look. Dates are 23 Mar to 16 Apr.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170416T042746_5C37_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170416T042746_5C37_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20170323T042745_D14E_S_1.final.jpg
Title: Re: PIG has calved
Post by: solartim27 on April 22, 2017, 07:32:41 AM
Here is a quick look over the past year.  See anything disturbing?  Click to animate.
(Tried a smaller version, 1 MB, it works!)(Oh well, I'm going to bed.  Here are the 2 pics, go full screen and toggle between them to your hearts content.  I was looking at the rifts between PIG and the Trib)

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170420T035503_D89B_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170420T035503_D89B_S_1.final.jpg)  (38 MB)

S1A_EW_GRDM_1SSH_20160331T045150_542F_S_1.final.jpg  (35 MB)

Title: Re: PIG has calved
Post by: Darvince on April 22, 2017, 07:35:16 AM
Forum software decided to not animate it for some reason, just to let you know.
Title: Re: PIG has calved
Post by: oren on April 22, 2017, 08:42:12 AM
Forum software decided to not animate it for some reason, just to let you know.
It's probably too large. If you limit to 700 pixel width it should work.
Edit: the last one works.
Title: Re: PIG has calved
Post by: solartim27 on May 03, 2017, 03:39:22 AM
Looks like the rift has made it to the notch at the top of the screen (to me).  Maybe it'll go with the next full moon?  Click to animate, (1.6 MB).
Apr 20 to May 2

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170502T035504_E082_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170502T035504_E082_S_1.final.jpg) (40 MB)

S1A_EW_GRDM_1SSH_20170420T035503_D89B_S_1.final.jpg (40 MB)
Title: Re: PIG has calved
Post by: Wipneus on May 07, 2017, 10:08:58 AM
The pixel noise in these Sentinel radar images make it hard to be sure. But it looks as some more opening/deepening at the ends of the crack.
Title: Re: PIG has calved
Post by: nukefix on May 07, 2017, 05:02:28 PM
The pixel noise in these Sentinel radar images make it hard to be sure. But it looks as some more opening/deepening at the ends of the crack.
Yes, if there's coherence InSAR would be the way to see the progress for sure.
Title: Re: PIG has calved
Post by: solartim27 on June 05, 2017, 09:09:41 PM
Wonderful. Here is a sequence 12 days apart, that means the Sentinel is in identical orbital position.
Resolution of the image is 120m/pixel, implying the width of the image is about 68km.
There are hi-res images available from the 24th and 25th
A nice view of the last breakup 2 years ago, the posts before and after this have some good shots as well. 

I believe we are right on track for a very similar collapse of the soon to be newly calved berg.  Here is a gif from 14 May to 5 Jun ( Click to animate 1.7 Mb) with two close ups of the notch areas, posted seperately.  Note the new calving in the north notch.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170605T041129_35BA_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170605T041129_35BA_S_1.final.jpg) (55 Mb)

S1A_EW_GRDM_1SSH_20170514T035505_4E16_S_1.final.jpg (40 Mb)
Title: Re: PIG has calved
Post by: solartim27 on June 05, 2017, 09:24:36 PM
Here are the smaller gifs, and a shameless self promotion, crack propagation looks like just before the last calving with the lower resolution
BYE BYE
Title: Re: PIG has calved
Post by: AbruptSLR on June 08, 2017, 05:51:39 PM
While it is obvious in other earlier images, I attach an image from June 6 2017 to highlight the fact that there is a crack that extends almost all the way through the width of the Southwest Tributary ice shelf; which will eventually lead to a major calving event from this critical ice shelf.
Title: Re: PIG has calved
Post by: solartim27 on June 19, 2017, 05:43:19 PM
Here is a gif from 7 Jun to 19 Jun of the southern PIG / Tributary boundary.  It looks to me that the rift has had a significant extension.  I wonder how far back the calving will go when that cork blows out.  Looking back at the calving 2 years ago, it went right as the rift came in line with the mountain peak to the north (not in this image), which is right where the rift is now.  (Click)

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170619T035507_39F5_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170619T035507_39F5_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20170607T035506_EDB2_S_1.final.jpg
Title: Re: PIG has calved
Post by: Wipneus on July 07, 2017, 07:35:09 PM
Signs of an upcoming calving. There is a new crack (left arrow) that became visible a few weeks ago and is getting clearer with every new image. Also the big crack that we have recognized a couple of years ago gets longer (second arrow) which could lead to a much bigger calving of course.
Title: Re: PIG has calved
Post by: solartim27 on July 13, 2017, 06:06:56 PM
Guess we'll have to wait at least one more lunar cycle.  Maybe with the new moon?
S1A_EW_GRDM_1SSH_20170713T035508_7376_S_1.final.jpg
S1A_EW_GRDM_1SSH_20170605T041129_35BA_S_1.final.jpg
Title: Re: PIG has calved
Post by: Ajpope85 on July 13, 2017, 06:34:41 PM
Is it usual to have large cracks propagating or large calving events in the winter?
Title: Re: PIG has calved
Post by: AbruptSLR on July 13, 2017, 07:28:53 PM
Is it usual to have large cracks propagating or large calving events in the winter?
It is usual to have calving events in the winter as sea ice offers little buttressing action against a large calving.  What is unusual is for the calving face on PIIS to located so far upstream.  This is a sign that global warming is advecting relatively warm water into the cavity beneath the ice shelf.  If/when the small ice shelf for the SW Tributary glacier also calves (possibly during the next major PIIS calving event in the next one to nine months) this should reduce buttressing on the SW Tributary glacier which would cause its ice flow velocity to increase.
Title: Re: PIG has calved
Post by: Wipneus on July 14, 2017, 11:58:16 AM
See my previous post on the 7th for an overview. This can not last long.
Title: Re: PIG has calved
Post by: silkman on July 14, 2017, 12:05:50 PM
Wipneus

What's the scale of this incipient event, relative to the Larsen C calving?
Title: Re: PIG has calved
Post by: Wipneus on July 14, 2017, 12:36:31 PM
Wipneus

What's the scale of this incipient event, relative to the Larsen C calving?

This one is 10m per pixel. So this image is 7kmx7km.
I do expect the eventual calving to be bigger than this, but nothing like Larsen C. The PIG calves far more often though, when the big crack (see my posting on 7/7) goes it will be the third big calving in the history of this thread.
Title: Re: PIG has calved
Post by: solartim27 on July 15, 2017, 05:02:40 PM
This tweet has a nice video from the ice bridge flight  from 11/2016, crossing from PIG to the SW Tributary
https://mobile.twitter.com/peter_neff/status/880067456131379203
Title: Re: PIG has calved
Post by: solartim27 on July 23, 2017, 07:57:53 PM
5 days, July 18 to 23.  Large motion, with big rift development behind the main crack.  Click to animate
S1A_EW_GRDM_1SSH_20170718T040320_7B12_S_1.final.jpg
S1A_EW_GRDM_1SSH_20170723T041131_F2E2_S_1.final.jpg
Title: Re: PIG has calved
Post by: Tor Bejnar on July 23, 2017, 11:56:22 PM
Given what we can see between the two images, I wonder what the inter-a-what-cha-ma-call-it-feromitor "interferometry" (used on Larsen C by Project MIDAS (http://www.projectmidas.org/feed.xml), showing details we couldn't see) shows.
Title: Re: PIG has calved
Post by: AbruptSLR on August 13, 2017, 07:02:46 PM
It is starting to look like the PIIS (and the SW Tributary Ice Shelf) may calve before the coming austral summer:

Title: Re: PIG has calved
Post by: Wipneus on September 13, 2017, 07:01:24 PM
An overview in 40m/pix (from the original 10m/pix) of the developing cracks in the Pine Island Glacier. Things are progressing very gradual without stalls and may continue to do so for a while.
The main crack, labeled "1" has widened to about 240m, twice the width of a year ago.
The crack "2" has developed for a few months now and is getting more visible by the week (width very small).
Crack "3" was clearly visible by the Sentinel 2 images, never as  clearly by S1. Hope we get to see optical images soon again.
The feature labeled "4" may be the next major crack, visibility still low but persistent over a few scans from the S1 satellites.

PS. Between the images the glacier moved 140m (measured at the great crack). That is about 11.5m/day. Slightly speeding up IIRC, but I really should repeat the measurement with images further apart.
Title: Re: PIG has calved
Post by: Wipneus on September 18, 2017, 04:58:00 PM
The visual season has begun in the Landsat offering.

Here is an animation in 45m/pix gving an overview of  the progress in 7 months. The images where shifted/rotated relative to each other to align at the upper edge of the "great crack".
Title: Re: PIG has calved
Post by: maga on September 22, 2017, 08:24:33 PM
Action at PIG!
Title: Re: PIG has calved
Post by: Aluminium on September 22, 2017, 11:37:27 PM
Two screenshots from EOSDIS (https://worldview.earthdata.nasa.gov/?p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2017-09-22&z=3&v=-1701592.9399274616,-358209.2301136656,-1526744.9399274616,-275137.2301136656).
Title: Re: PIG has calved
Post by: oren on September 22, 2017, 11:53:55 PM
I know it's been expected on this forum for months but it's still jaw-dropping.
I believe PIG is in record retreat and the SW tributary has lost major buttressing (can't verify this atm though).
Title: Re: PIG has calved
Post by: AbruptSLR on September 23, 2017, 12:26:34 AM
I know it's been expected on this forum for months but it's still jaw-dropping.
I believe PIG is in record retreat and the SW tributary has lost major buttressing (can't verify this atm though).

I concur that the PIIS is in record retreat, but it is not clear to me that the SW tributary has yet lost major buttressing.
Title: Re: PIG has calved
Post by: maga on September 23, 2017, 11:08:13 AM
I also don't think that the SW tributary did already loose a lot of buttressing. I'm rather more worried about the front of it breaking away. I imagine PIG speeding up as a consequence and the western shear zone slipping through the new opening (where currently the half-calved berg sits). This should rapidly weaken the western shelf of PIG even more and eventually it won't be able to keep up pressure on PIG which in turn will retreat at least until the end of the bay somewhere around the position where the grounding line is plotted in the Modis pictures. From there I expect slower retreat in a different style, similar to Jakobshavn.
Title: Re: PIG has calved
Post by: maga on September 23, 2017, 02:36:34 PM
Polarview has it as well now. Interesting crack across the berg. Must have been quite some pressure on the western tip!
Title: Re: PIG has calved
Post by: AbruptSLR on September 23, 2017, 06:42:22 PM
I also don't think that the SW tributary did already loose a lot of buttressing. I'm rather more worried about the front of it breaking away. I imagine PIG speeding up as a consequence and the western shear zone slipping through the new opening (where currently the half-calved berg sits). This should rapidly weaken the western shelf of PIG even more and eventually it won't be able to keep up pressure on PIG which in turn will retreat at least until the end of the bay somewhere around the position where the grounding line is plotted in the Modis pictures. From there I expect slower retreat in a different style, similar to Jakobshavn.

I generally concur with your concerns, but it would be helpful if you would replace the term 'western' with 'southwestern'.  Also, the 'front' of the SW tributary glacier is the Southwest Tributary Ice Shelf, STIS.
Title: Re: PIG has calved
Post by: Wipneus on September 23, 2017, 07:34:24 PM
Let me try an animation of the event (did not work in another thread).
Title: Re: PIG has calved
Post by: oren on September 24, 2017, 12:16:05 AM
I believe PIG is in record retreat and the SW tributary has lost major buttressing (can't verify this atm though).
Turns out verification is important... the last major calving of the PIG happened around Aug 1st 2015 (If I am not mistaken). Turns out the new PIG calving front near the SW tributary is at the same location as the front in 2015, and in general the whole front is in record retreat but just barely. Apologies for the lousy resolution. And for unverified assumptions.
In addition, can the honored folks here confirm that the new calving is based on a crack that has been developing since 2015? This was my impression as I browsed up-forum.
If the past is any indication, one side of the new berg - on the left in the animation - could become grounded for a while. Will be interesting to watch.
Title: Re: PIG has calved
Post by: AbruptSLR on September 24, 2017, 04:16:45 AM
Turns out verification is important... the last major calving of the PIG happened around Aug 1st 2015 (If I am not mistaken).

I believe that last major calving of the PIIS occurred some time between July 23 and July 30, 2015.
Title: Re: PIG has calved
Post by: oren on September 24, 2017, 08:34:58 AM
Twitter link provides a better animation as well as a reminder of previous calving front locations.
https://twitter.com/StefLhermitte/status/911722449225515008 (https://twitter.com/StefLhermitte/status/911722449225515008)
And an animation (posted Jan 17) showing rift progression since 2015.
https://twitter.com/StefLhermitte/status/826364887106457600 (https://twitter.com/StefLhermitte/status/826364887106457600)
Can anyone estimate the next breaking point on the main PIG? I can't see any new crack coming up.
Title: Re: PIG has calved
Post by: Jim Hunt on September 24, 2017, 09:19:10 AM
You left out this one oren:

https://twitter.com/StefLhermitte/status/911712305049751558

Crowdsourcing beats automation any day of the week!
Title: Re: PIG has calved
Post by: Wipneus on September 24, 2017, 07:20:41 PM
In addition, can the honored folks here confirm that the new calving is based on a crack that has been developing since 2015? This was my impression as I browsed up-forum.

Yes. The major crack involved in this event was noticed some time before the 2015 event. It can be found tracing this thread back.

There is a possible new crack that I noticed in this post (https://forum.arctic-sea-ice.net/index.php/topic,429.msg128825.html#msg128825). It is also visible on the latest clear Landsat image, but very vague: the snow must be thick and the crack thin. See attached image which has undergone some contrast enhancements.

If(!) the crack develops into the new calving, it will be smaller than the three previous ones. About one third I would say.
Title: Re: PIG has calved
Post by: A-Team on September 24, 2017, 10:07:49 PM
visible on the latest clear Landsat image, but very vague: the snow must be thick and the crack thin.
Indeed it's hard to draw out that feature ....
Title: Re: PIG has calved
Post by: AbruptSLR on September 26, 2017, 03:27:14 PM
The linked article highlights the role of warm ocean water in causing the PIIS to thin and accelerate; however, they do not acknowledge: (1) the interaction between the PIIS and the SW Tributary Ice Shelf; nor (2) the potential influence of hydrofracturing (as discussed by DeConto & Pollard 2016) on accelerating calving as GMSTA approaches 2.7C:

Title: "Yet Another Giant Iceberg Has Broken Free From Antarctic"

https://gizmodo.com/yet-another-giant-iceberg-has-broken-free-from-antarcti-1818729430

Extract: "Shuman also confirmed that the rifts are forming in the center of the glacier and extending out toward the edges. This means that the rifts are forming far inland, likely the result of warm ocean water rubbing against the base of the glacier. This may explain why the calving events are happening with increased frequency (the speed of the glacier’s flow towards the sea is increasing, and it’s now moving at about 2.5 miles (4 km) per year), and why PIG appears to be thinning (the rate of thinning has quadrupled since the mid 1990s). If this current rate of thinning continues, the entire main trunk of the glacier could be afloat in about 100 years."
Title: Re: PIG has calved
Post by: AbruptSLR on October 06, 2017, 12:26:30 AM
Here is a Landsat 8 image from Sept 28 2017

https://earthobservatory.nasa.gov/IOTD/view.php?id=91066
Title: Re: PIG has calved
Post by: AbruptSLR on October 06, 2017, 12:42:54 AM
Attached is a Sentinel-1 image of the PIIS from Oct 4 2017, that clearly indicates that Iceberg B-44 is not pinned and is floating away from the ice shelf.
Title: Re: PIG has calved
Post by: Wipneus on October 11, 2017, 06:29:21 PM
The calving breaks, partly along known cracks.
Title: Re: PIG has calved
Post by: Wipneus on October 14, 2017, 03:59:31 PM
Also the Sentinel 2 season has begun. Breathtaking quality, but too late for the latest calving.
Title: Re: PIG has calved
Post by: Shared Humanity on October 14, 2017, 07:08:11 PM
The detail (windswept snow across the calved iceberg, the shape and condition of the small bergs, some toppled over, others upright, the shadows cast by the sun, low in the horizon, the icy blue patches of water, tinted by the crumbling and spreading out of ancient ice of the glacier) is amazing.
Title: Re: PIG has calved
Post by: P-maker on October 14, 2017, 08:13:01 PM
Shared Humanity.

Indeed - niveo-aeolian glacio-mechanics seems to be a new subject of rising importance. The drifting away of icebergs is also the result of aeolian processes. The infilling of the two or three crevasses already visible up-stream is a complex niveo-aeolian phenomenon. At some stage - when the ice cliff becomes high enough - the mechanics will take over.
Title: Re: PIG has calved
Post by: Wipneus on October 15, 2017, 11:32:33 AM
The way a calving crumbles.
Title: Re: PIG has calved
Post by: steve s on October 16, 2017, 10:28:52 AM
I agree, Shared Humanity. Beautiful.
Title: Re: PIG has calved
Post by: Shared Humanity on October 16, 2017, 03:54:10 PM
The shadows cast by the sun, low in the horizon, on the Sentinel 2 image and this latest crumbling suggests to me that the PIG is undergoing dramatic thinning. If you look at the upper left portion of the Sentinel 2 image, the shadow shrinks dramatically as you move towards the center of the berg just recently calved. Is there some way to calculate the freeboard of the thinner section and determine the thickness of the shelf here? Also, on the 2nd image, there are pronounced depressions (3 at least, perhaps as many as 5) that run through the ice shelf and terminate on the calving face exactly where the crumbling on the berg is occurring. Wouldn't these suggest canyons have formed on the underside of the shelf by warm waters flowing to the open sea? If this is so, the leading edge of the PIG may be far more susceptible to collapse than it would appear.
Title: Re: PIG has calved
Post by: Shared Humanity on October 16, 2017, 04:02:11 PM
Wipneus....

Could you capture a Sentinel 2 image of the calved berg where these apparent depressions exist closer to the center of the berg) so that we can determine whether the shadows confirm the existence of the depressions? Also if these are caused by undulating height of the ice shelf is there any other reason than thinning of the glacier that would cause this? Perhaps scouring of snow on the surface of the glacier by winds?
Title: Re: PIG has calved
Post by: oren on October 18, 2017, 12:41:55 AM
The rapid crumbling of the PIIS calf is scary. As if it was barely holding itself together before the calving.
p.s. the animation also shows another (very minor) calving at the eastern tip.
Title: Re: PIG has calved
Post by: Wipneus on October 18, 2017, 08:37:09 AM
Wipneus....

Could you capture a Sentinel 2 image of the calved berg where these apparent depressions exist closer to the center of the berg) so that we can determine whether the shadows confirm the existence of the depressions?

I have uploaded the full image at
https://drive.google.com/open?id=0B8NUHa4P2gmlNzVrcldTUHQ1TXM

Download this in a sufficiently powerful PC (file size is about 600MB) and view with the Gimp or some other capable software.

Title: Re: PIG has calved
Post by: Wipneus on October 25, 2017, 06:48:02 PM
More crumbling...
Title: Re: PIG has calved
Post by: Shared Humanity on October 25, 2017, 08:10:04 PM
It would seem that most of the cracks are occurring in areas where the berg and ice shelf show depressions. Are these snow covered depressions actually deep fissures hidden from view?
Title: Re: PIG has calved
Post by: Adam Ash on October 26, 2017, 03:51:38 AM
Interesting paper on ice-cliff instability, which presumably has relevance to all ocean-terminating glaciers.

Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks
http://www.nature.com/nature/journal/v550/n7677/full/nature24458.html?WT.ec_id=NATURE-20171026&spMailingID=55217903&spUserID=NzE3MDU3OTQ1MDMS1&spJobID=1264650535&spReportId=MTI2NDY1MDUzNQS2

and an illustration of the concepts..
http://www.nature.com/nature/journal/v550/n7677/fig_tab/nature24458_F4.html

and all the figures at:
http://www.nature.com/nature/journal/v550/n7677/fig_tab/nature24458_ft.html

From the abstract...
'From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today8, 9, which would produce wide, flat-based plough marks10 or toothcomb-like multi-keeled plough marks11, 12. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels.'
'Our findings demonstrate the effective operation of Marine ice-cliff instability (MICI) in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet.'
Title: Re: PIG has calved
Post by: Adam Ash on October 26, 2017, 03:54:36 AM
More crumbling...

Is this crumbling an indication that the ice generally has a lower structural strength than previously, where tabular bergs would hold together?  If so, this would suggest that the ice is warmer than before.  Unsurprising, if that is the case, tho troubling too.
Title: Re: PIG has calved
Post by: sidd on October 26, 2017, 04:36:02 AM
Thanks for the link to the Wise paper. Nice. I attach Fig 4

sidd
Title: Re: PIG has calved
Post by: oren on October 26, 2017, 08:41:15 AM
Thank you. Highly interesting, a pity it's pay-walled.
A MICI model supported by actual evidence on the seafloor, a strong argument indeed.
Title: Re: PIG has calved
Post by: Wipneus on October 28, 2017, 11:46:32 AM
The disintegration of the PIG calving is subject of today's NASA Earth Observatory "image of the day":
https://earthobservatory.nasa.gov/IOTD/view.php?id=91203

One consequence is:
None of the fractured pieces are large enough to be named and tracked by the U.S. National Ice Center, which has removed B-44 from their table of tracked bergs.

That was quick.
Title: Re: PIG has calved
Post by: solartim27 on October 31, 2017, 05:44:22 PM
Nice time lapse video in this article.  Also includes Thwaites.
https://www.nytimes.com/interactive/2017/10/26/climate/antarctica-glaciers-melt.html?smid=tw-nytimes&smtyp=cur&_r=0
The animation above shows Pine Island glacier flowing into the Amundsen Sea from 2014 to 2017. Twice in that period, the glacier released an iceberg larger than 100 square miles.
Title: Re: PIG has calved
Post by: FishOutofWater on October 31, 2017, 06:20:17 PM
Whoa, Wip, that was much too quick. Periodic formation of icebergs happened before the effects of climate change hit Antarctica, but this rapid disintegration looks like something else altogether. It has apparently disintegrated along lines of weakness caused by extension during flow. I suspect that there has been a substantial amount of melting on the underside of the glacier.

This does not bode well for the long term stability of PIG.
Title: Re: PIG has calved
Post by: oren on November 01, 2017, 12:47:37 AM
Nice time lapse video in this article.  Also includes Thwaites.
https://www.nytimes.com/interactive/2017/10/26/climate/antarctica-glaciers-melt.html?smid=tw-nytimes&smtyp=cur&_r=0
The animation above shows Pine Island glacier flowing into the Amundsen Sea from 2014 to 2017. Twice in that period, the glacier released an iceberg larger than 100 square miles.
Thanks. These NYT animations are superb, especially the Thwaites one. The Thwaites discharge area is very "messy", and the animation helps understand what is going on where in there.
Title: Re: PIG has calved
Post by: Wipneus on November 20, 2017, 06:35:49 PM
Good optical images are scarce at the moment: Sentinel 2 images have not been uploaded since the beginning of October while Landsat images are mostly cloudy. This Landsat 8 image from the 17th is still hazy, but the new crack can yet easily made visible by enhancing the contrast.
Title: Re: PIG has calved
Post by: crandles on November 20, 2017, 07:49:15 PM
Antarctic glacier's rough belly exposed

The melting Antarctic ice stream that is currently adding most to sea-level rise may be more resilient to change than previously recognised.

New radar images reveal the mighty Pine Island Glacier (PIG) to be sitting on a rugged rock bed populated by big hills, tall cliffs and deep scour marks.

Such features are likely to slow the ice body’s retreat as the climate warms, researchers say.

http://www.bbc.co.uk/news/science-environment-42052072

Nature Communications (https://www.nature.com/articles/s41467-017-01597-y.epdf?referrer_access_token=ruTwQL7bm2ZNg67i5ZzkeNRgN0jAjWel9jnR3ZoTv0OnMuUNNrJ_9P29O_jkfU5TYH2pc7TLJc2HQAlISzLbMo5UYT2AEZSB5GvbhjdXezVo9WVlLlOSdCyRfenno7ZpJUPrn75OeFED3pxNWU2Ef-Klm0hFZwLG78rupnIVTHnpXnwO1mEh-Sjk_2xt4Rr83FVvVr4_K4hXRNpsMLSgtC9cWcZVkjrwb6YYBb5z1zo%3D&tracking_referrer=www.bbc.co.uk)

Diverse landscapes beneath Pine Island Glacier influence ice flow

The retreating Pine Island Glacier (PIG), West Antarctica, presently contributes ~5–10% of global sea-level rise. PIG’s retreat rate has increased in recent decades with associated thinning migrating upstream into tributaries feeding the main glacier trunk. To project future change  requires  modelling  that  includes  robust  parameterisation  of  basal  traction,  the resistance to ice flow at the bed. However, most ice-sheet models estimate basal traction from satellite-derived surface velocity, without a priori knowledge of the key processes from which it is derived, namely friction at the ice-bed interface and form drag, and the resistance to ice flow that arises as ice deforms to negotiate bed topography. Here, we present high-resolution maps, acquired using ice-penetrating radar, of the bed topography across parts of PIG. Contrary to lower-resolution data currently used for ice-sheet models, these data show a contrasting topography across the ice-bed interface. We show that these diverse subglacial landscapes have an impact on ice flow, and present a challenge for modelling ice-sheet evolution and projecting global sea-level rise from ice-sheet loss.
Title: Re: PIG has calved
Post by: AbruptSLR on November 20, 2017, 08:24:00 PM
Such features are likely to slow the ice body’s retreat as the climate warms, researchers say.

If one only considers basal slide of the PIG, then the basal roughness of PIG's bed identified in the linked reference is good news, as it may slow future ice mass loss.  On the other hand, such basal roughness may do little to slow ice mass loss associated with any future cliff failures that PIG may experience in the coming decades, as Wise et al. (2017) demonstrates happened in the not too distant past:

Wise et al. (2017), "Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks", Nature 550, 506-510, doi:10.1038/nature24458

https://www.nature.com/articles/nature24458

Extract: "From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today, which would produce wide, flat-based plough marks or toothcomb-like multi-keeled plough marks. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels.
...
Our findings demonstrate the effective operation of Marine ice-cliff instability (MICI) in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet."

See also:

http://glacierhub.org/2017/11/20/roundup-ice-cliff-instability-buffers-glacial-retreat/
Title: Re: PIG has calved
Post by: Susan Anderson on November 20, 2017, 09:34:47 PM
Fascinating graphic and exposition. If there are more big rapid breakups, I'd guess (and it is only a guess) that means deeper iceberg breakoffs and more scraping, is that right?
Title: Re: PIG has calved
Post by: AbruptSLR on November 20, 2017, 10:52:01 PM
Fascinating graphic and exposition. If there are more big rapid breakups, I'd guess (and it is only a guess) that means deeper iceberg breakoffs and more scraping, is that right?

Susan,
The topic of ice cliff failures and hydrofracturing has been discussed extensively in other threads, so I will only touch on this topic here.  The first attached image (see also the associated caption) shows Pollard et al. (2015)'s criteria for cliff failure in a marine glacier without hydrofracturing (I note that DeConto indicates that a lot of hydrofracturing will occur in key portions of West Antarctica well before GMSTA gets to 2.7C).  So without hydrofracturing cliff failures (at the grounding line) roughly occur when the portion of the cliff face above the water line equals, or exceeds, about 90 to 100m, in a water depth on the order of 800m; once the ice shelf has collapsed.

Once the Pine Island Ice Shelf collapses (say due to hydrofracturing if/when GMSTA nears 2.7C, which might be as soon as 2040 per the second attached image from Friedrich et al. (2016), assuming BAU warming until at least 2040), then there could be a lot of cliff failures of the PIG as at its grounding line it currently exceeds Pollard et al (2015)'s criteria.  This might result in an extensive ice mélange in front of the PIG, which might increase bottom gouging and might partially buttress the face of the PIG (thus temporarily stopping more calving).  However, I note that the ice mélange in front of the Jacobshavn Glacier in Greenland only provides limited buttressing of calving from its face.

Pollard et al (2015), https://doi.org/10.1016/j.epsl.2014.12.035

http://www.sciencedirect.com/science/article/pii/S0012821X14007961

Caption: "Fig. 2. Schematic cross-sections of an ice sheet approaching cliff failure. Ice flow is from left to right, from grounded ice to floating shelf. M = surface liquid runoff into crevasses. C = calving. O = oceanic basal melt. F = deformational flow across the grounding line. Red arrows show possible grounding-line movement. (a) With substantial ice shelf, and shallow surface slopes in the grounding zone. (b) After strong warming (large M,C,O) with the shelf nearly removed but still allowing shallow slopes. (c) With the shelf completely removed, exposing a vertical cliff > ∼100 m above sea level that undergoes structural failure, causing very rapid grounding-line retreat. Note that “cliff” failure can also occur at grounding lines with ice shelves, if the ice shelf provides little or no buttressing. It can occur in shallower depths than shown if the ice column at the grounding line is weakened by melt-driven hydrofracturing M"

Best regards,
ASLR
Title: Re: PIG has calved
Post by: Wipneus on December 11, 2017, 06:16:09 PM
On the SW side new cracks have formed.
Title: Re: PIG has calved
Post by: AbruptSLR on December 11, 2017, 06:50:26 PM
On the SW side new cracks have formed.

Not to sound like a Jeremiah, but this new cracking pattern in the PIIS looks to me like it could be associated with a coming major calving of the Southwest Tributary Ice Shelf; which might contribute to an eventual acceleration of the Southwest Tributary Glacier ice flow velocities.
Title: Re: PIG has calved
Post by: FredBear on December 12, 2017, 02:15:52 AM
"Jeremiah", the movements of glacier, icebergs and cracks look too fast to bode well, I'm afraid   .   .   .   (even if the Sept. 22 calving only moved the calving face back to the 2015 position).
Title: Re: PIG has calved
Post by: Susan Anderson on December 22, 2017, 05:22:20 AM
New from Earth Observatory https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=91470&src=nha (https://earthobservatory.nasa.gov/NaturalHazards/view.php?id=91470&src=nha)

Pine Island Iceberg Under the Midnight Sun
(https://eoimages.gsfc.nasa.gov/images/imagerecords/91000/91470/pineisland_oli_2017349.jpg)
acquired December 15, 2017 [note: to download large image (6 MB, JPEG, 5000x5000) go to link]

In September 2017, a new iceberg calved from Pine Island Glacier—one of the main outlets where the West Antarctic Ice Sheet flows into the ocean. Just weeks later, the berg named B-44 shattered into more than 20 fragments.

On December 15, 2017, the Operational Land Imager (OLI) on Landsat 8 acquired this natural-color image of the broken berg. An area of relatively warm water, known as a polyna, has kept the water ice free between the iceberg chunks and the glacier front. NASA glaciologist Chris Shuman thinks the polynya’s warm water could have caused the rapid breakup of B-44.

The image was acquired near midnight local time. Based on parameters including the azimuth of the Sun and its elevation above the horizon, as well as the length of the shadows, Shuman has estimated that the iceberg rises about 49 meters above the water line. That would put the total thickness of the berg—above and below the water surface—at about 315 meters.
Title: Re: PIG has calved
Post by: Wipneus on December 23, 2017, 01:13:24 PM
Detail of the widening SW crack.
Title: Re: PIG has calved
Post by: oren on December 23, 2017, 10:49:32 PM
Looks like a lot of widening given it's just 9 days between the images.
Title: Re: PIG has calved
Post by: maga on December 26, 2017, 03:57:38 PM
The picture in Susan's entry shows several more cracks. They can also be seen from time to time in Aqua (Modis) pictures but not in such detail. I marked some of them.
Title: Re: PIG has calved
Post by: Grygory on January 10, 2018, 10:02:50 PM
Amazing how grow new crack in pine island glacier
http://www.polarview.aq/images/106_S1jpgsmall/201801/S1A_IW_GRDH_1SSH_20180110T043545_BF1A_S_1.jpg but what's more amazing is what's happening at the next glacier:
http://www.polarview.aq/images/106_S1jpgsmall/201801/S1A_IW_GRDH_1SSH_20180110T043610_7729_S_1.jpg -This season mealting will by propobly rekord in this region Antarctic
if not wholly
Title: Re: PIG has calved
Post by: Tealight on January 13, 2018, 01:30:48 PM
Sentinel2 started acquiring images of Antarctica again.

Click on the first image for full resolution of the new crack.

The second image shows one of the rifts 20km upstream, which has some ice-free spots in it. I'm wondering if the ocean heat was enough to melt the ice locally. There the ice can't just drift away like the calving front.
Title: Re: PIG has calved
Post by: solartim27 on January 13, 2018, 04:11:07 PM
The second image shows one of the rifts 20km upstream, which has some ice-free spots in it. I'm wondering if the ocean heat was enough to melt the ice locally. There the ice can't just drift away like the calving front.
I believe it's much to thick to melt through in a single spot.  Looks to me that it's from rifting and downstream bergs moving faster than the still attached parts.  With all the new rifts on that side, I think well see more frequent smaller calving of PIG.
Title: Re: PIG has calved
Post by: solartim27 on January 14, 2018, 01:22:02 AM
Nice gif from Landsat 8, dates 26 Dec to 11 Jan on this tweet
https://twitter.com/StefLhermitte/status/951967405890310145
Title: Re: PIG has calved
Post by: Bernard on January 14, 2018, 10:58:42 AM
Nice gif from Landsat 8, dates 26 Dec to 11 Jan on this tweet
https://twitter.com/StefLhermitte/status/951967405890310145
Impressive images. Not only the extension of the crack, but the rapid move of the chunks of desintegrated B44. New calving by the end of this month, I would bet.
Title: Re: PIG has calved
Post by: ghoti on January 14, 2018, 04:18:24 PM
His pinned tweet is also very impressive: PIG, the movie

https://twitter.com/StefLhermitte/status/918875349945126912