Pine Island Glacier (PIG) Calving and Discussion

[AbruptSLR]

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).

[Wipneus]

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)

[Wipneus]

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.

[A-Team]

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?

[crandles]

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?

[plinius]

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.

[AbruptSLR]

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.

[A-Team]

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?

[AbruptSLR]

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

[A-Team]

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 

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

[A-Team]

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

[Wipneus]

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)

[Wipneus]

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.

[A-Team]

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

[A-Team]

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

[solartim27]

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.

[A-Team]

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/

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.

[A-Team]

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://svs.gsfc.nasa.gov/cgi-bin/search.cgi?contentType=hw
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
LC82291142015048LGN00   Center -75.90228, -96.94265   17 Feb 15 clear #422
LC82291142015032LGN00   Center -75.90227, -96.96392   01 Feb 15 cloudy
LC82291142015016LGN00   Center -75.90193, -96.97173   16 Jan 15 cloudy
LC82291142014365LGN00   Center -75.90196, -96.96660   31 Dec 14 clear #422
LC82291142014349LGN00   Center -75.90200, -96.98514   15 Dec 14 clear
LC82291142014333LGN00   Center -75.90227, -97.00789   29 Nov 14 cloudy
LC82291142014317LGN00   Center -75.90203, -97.01751   13 Nov 14 cloudy
LC82291142014301LGN01   Center -75.90205, -97.01075   28 Oct 14 cloudy
LC82291142014285LGN00   Center -75.90214, -97.03389   12 Oct 14 cloudy
LC82291142014269LGN00   Center -75.90196, -97.02146   26 Sep 14 cloudy
LC82291142014077LGN00   Center -75.90199, -96.86891   18 Mar 14 cloudy
LC82291142014061LGN00   Center -75.90201, -96.85982   02 Mar 14 cloudy
LC82291142014045LGN00   Center -75.90205, -96.88937   14 Feb 14 cloudy
LC82291142014029LGN00   Center -75.90213, -96.91992   29 Jan 14 cloudy
LC82291142014013LGN00   Center -75.90204, -96.91701   13 Jan 14 clear #422
LC82291142013362LGN00   Center -75.90230, -96.95275   28 Dec 13 cloudy
LC82291142013346LGN00   Center -75.90202, -96.96745   12 Dec 13 cloudy
LC82291142013330LGN00   Center -75.90190, -96.95394   26 Nov 13 cloudy
LC82291142013314LGN00   Center -75.90202, -96.96959   10 Nov 13 cloudy

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
S1A_IW_GRDH_1SSH_20150919    T050725_20150919    T050754_007779_00AD24_BFB8
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
S1A_IW_GRDH_1SSH_20150711    T080551_20150711    T080616_006760_00911F_BE52
S1A_IW_GRDH_1SSH_20150701    T043512_20150701    T043537_006612_008D15_FAF8
S1A_IW_GRDH_1SSH_20150629    T080526_20150629    T080551_006585_008C53_5F2A
S1A_IW_GRDH_1SSH_20150617    T080525_20150617    T080550_006410_008769_DC22
S1A_IW_GRDH_1SSH_20150606    T035431_20150606    T035456_006247_0082C9_78F0
S1A_IW_GRDH_1SSH_20150514    T043521_20150514    T043546_005912_0079E2_6135
S1A_IW_GRDH_1SSH_20150502    T043452_20150502    T043521_005737_0075DF_2D8C
S1A_IW_GRDH_1SSH_20150420    T043520_20150420    T043545_005562_0071E3_5E98
S1A_IW_GRDH_1SSH_20150408    T043519_20150408    T043544_005387_006D8A_7DC3
S1A_IW_GRDH_1SSH_20150404    T050717_20150404    T050746_005329_006C0A_ED52
S1A_IW_GRDH_1SSH_20150323    T050746_20150323    T050811_005154_0067F8_31A3
S1A_IW_GRDH_1SSH_20150314    T084602_20150314    T084627_005025_0064D5_7F14
S1A_IW_GRDH_1SSH_20150303    T043450_20150303    T043519_004862_0060F2_3DE0
S1A_IW_GRDH_1SSH_20150219    T043519_20150219    T043544_004687_005CB0_749C
S1A_IW_GRDH_1SSH_20150215    T050717_20150215    T050745_004629_005B4D_BCCC
S1A_IW_GRDH_1SSH_20150203    T050746_20150203    T050811_004454_005750_7F80
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

[AbruptSLR]

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.

[nukefix]

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...

[AbruptSLR]

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

[AbruptSLR]

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/spaceinimages/Images/2014/08/Antarctic_peninsula_ice-sheet_change

[A-Team]

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.

[P-maker]

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

and a whole series here:
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…

[nukefix]

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

[AbruptSLR]

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.

[A-Team]

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.

[P-maker]

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.

[nukefix]

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.

[AbruptSLR]

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

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.

[A-Team]

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?

[A-Team]

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/

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.

[AbruptSLR]

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

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/

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."

[AbruptSLR]

As I believe that the Sentinel 1A images use radar they should not show snow induced sastrugi, but rather the crevasses beneath the snow.

[A-Team]

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/

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/

[Sleepy]

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

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

[AbruptSLR]

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

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

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

[A-Team]

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.

[A-Team]

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).

[P-maker]

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.

[AbruptSLR]

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/
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.

[AbruptSLR]

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

[AbruptSLR]

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


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."

[oren]

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


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.

[AbruptSLR]

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.

[A-Team]

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....

[nukefix]

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..

[P-maker]

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.

[A-Team]

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

[AbruptSLR]

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

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

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

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

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

"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.""