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Wipneus

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Re: PIG has calved
« Reply #200 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.
 
« Last Edit: October 24, 2014, 06:52:56 AM by Wipneus »

Lennart van der Linde

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Re: PIG has calved
« Reply #201 on: October 23, 2014, 06:43:50 PM »
Wipneus, thanks. How many pixels/km from that huge crack to the sea?

Wipneus

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Re: PIG has calved
« Reply #202 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.

Wipneus

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Re: PIG has calved
« Reply #203 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.



AbruptSLR

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Re: PIG has calved
« Reply #204 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.
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sidd

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Re: PIG has calved
« Reply #205 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

AbruptSLR

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Re: PIG has calved
« Reply #206 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

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
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icefest

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Re: PIG has calved
« Reply #207 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.


Here is plain edit, without my drawings: http://puu.sh/cqxb5/dd24c1b596.jpg
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AbruptSLR

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Re: PIG has calved
« Reply #208 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
 
Best,
ASLR
« Last Edit: October 26, 2014, 04:05:58 PM by AbruptSLR »
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icefest

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Re: PIG has calved
« Reply #209 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.
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AbruptSLR

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Re: PIG has calved
« Reply #210 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
« Last Edit: October 27, 2014, 02:57:34 AM by AbruptSLR »
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icefest

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Re: PIG has calved
« Reply #211 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.
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AbruptSLR

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Re: PIG has calved
« Reply #212 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
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icefest

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Re: PIG has calved
« Reply #213 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 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
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AbruptSLR

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Re: PIG has calved
« Reply #214 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
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AbruptSLR

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Re: PIG has calved
« Reply #215 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.
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AbruptSLR

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Re: PIG has calved
« Reply #216 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:
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icefest

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Re: PIG has calved
« Reply #217 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.

Image from ASLR
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icefest

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Re: PIG has calved
« Reply #218 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.
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AbruptSLR

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Re: PIG has calved
« Reply #219 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
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AbruptSLR

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Re: PIG has calved
« Reply #220 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


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

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


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.
 
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
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AbruptSLR

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Re: PIG has calved
« Reply #221 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.
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AbruptSLR

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Re: PIG has calved
« Reply #222 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.
« Last Edit: October 29, 2014, 06:46:57 PM by AbruptSLR »
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crandles

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Re: PIG has calved
« Reply #223 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.  ;)

AbruptSLR

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Re: PIG has calved
« Reply #224 on: October 29, 2014, 12:26:16 AM »
Thanks for the catch.  I have changed "red curse" to "red curve"
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AbruptSLR

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Re: PIG has calved
« Reply #225 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
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AbruptSLR

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Re: PIG has calved
« Reply #226 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.
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AbruptSLR

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Re: PIG has calved
« Reply #227 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.
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Wipneus

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Re: PIG has calved
« Reply #228 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).

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Re: PIG has calved
« Reply #229 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)

AbruptSLR

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Re: PIG has calved
« Reply #230 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
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/
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.
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AbruptSLR

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Re: PIG has calved
« Reply #231 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.
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Re: PIG has calved
« Reply #232 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:

Reality is merely an illusion, albeit a very persistent one - Albert Einstein

Wipneus

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Re: PIG has calved
« Reply #233 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.
« Last Edit: November 09, 2014, 08:54:24 AM by Wipneus »

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Re: PIG has calved
« Reply #234 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)

Wipneus

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Re: PIG has calved
« Reply #235 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.

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Re: PIG has calved
« Reply #236 on: November 09, 2014, 10:38:01 AM »
It looks like the crack will expand further between the red lines?

Have a ice day!

AbruptSLR

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Re: PIG has calved
« Reply #237 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
« Last Edit: November 09, 2014, 12:18:22 PM by AbruptSLR »
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Jim Hunt

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Re: PIG has calved
« Reply #238 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?
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

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Re: PIG has calved
« Reply #239 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".

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Re: PIG has calved
« Reply #240 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 :)

AbruptSLR

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Re: PIG has calved
« Reply #241 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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: PIG has calved
« Reply #242 on: November 10, 2014, 03:40:30 AM »
Thanks Hunter, always at the right spot ;)
Have a ice day!

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Re: PIG has calved
« Reply #243 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
« Last Edit: November 10, 2014, 06:02:55 AM by AbruptSLR »
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Re: PIG has calved
« Reply #244 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

 

AbruptSLR

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Re: PIG has calved
« Reply #245 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/suppl/2014/01/02/science.1244341.DC1/Dutrieux.SM.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."
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AbruptSLR

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Re: PIG has calved
« Reply #246 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.
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AbruptSLR

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Re: PIG has calved
« Reply #247 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).
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Re: PIG has calved
« Reply #248 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.
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AbruptSLR

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Re: PIG has calved
« Reply #249 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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson