Pine Island Glacier (PIG) Calving and Discussion

[paolo]

Baking,

In order to not create confusion in this forum, until now the names R1, R2, R3, ... have been used to designate the rifts opening to the Main Ice Shelf, from the first one further downstream, to the others progressing upstream, and having the potential to traverse it completely. In particular the notation R2 has already been used in this forum for one of the two major rifts related to the future calving (see attachment) and the one you call "R2" is only one of the rifts that are opening in the future iceberg and for which another notation should be used so as not to induce confusion.

For the rest I agree that the southern margin exerts a major constraint on the whole width of the glacier and that the northern margin is still strongly resisting and will resist for some time, which will lead to a breakup of the future iceberg into several pieces.

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[baking]

Sorry, I guess I was confused by all the Rs.  May I suggest R0 and R1 for the northernmost (and downstream) transverse rifts?

[paolo]

Baking, your suggestion seems very reasonable to me... 

From now on R3 is a transverse rift and its progression is really impressive: 4 km in 10 days ...

"R4" for the moment is still marginal and only potentially transverse, in your opinion it should be noted differently and keep Rx only for the rift surely transverse?

If in the future a new transverse rift is formed between two already named rifts, for example R3 and R4, how to name it? We could, as for software versions, note it with "R3.5", what do you think? 

[paolo]

R0, R1, R2, R3..., it's no longer a glacier, it's sliced salami... 

[baking]

If you look closely, the marginal rift you have been calling R3 is actually almost connected to a transverse rift that began between 1 and 2 years ago as one of a series of four, near the margin, but not in the margin.  So in a sense, your R3 "got lucky" but that doesn't mean it makes sense to number every marginal rift because most will amount to nothing.

[blumenkraft]

How about that?

We call rifts that develop in the middle of the shelf R$number where $number=1 is the first one from the calving front.

And we call rifts that develop from the margins MR$number.

That would mean the R0 is now R1 and R3 is now MR1.

[blumenkraft]

Actually, R0 is R2 because there is another crack before it.

[paolo]

Blumenkraft,

The naming of rifts arises from the need to communicate with each other and to follow it over time (and it is very useful).

It must be unique and must not be changed over time.

And it should only concern the really important rifts leading to calving : we are not going to name all rifts, crevasses, which would only lead to total confusion and complete uselessness.

So R1 and R2 should remain R1 and R2.

R0 which concerns the future bursting of the iceberg and which concerns the whole iceberg remains R0, bat we could possibly name it R0.5 in the event that we feel the need to name other rifts in the future iceberg (which seems difficult to me, already R0 has a much lesser usefulness than R1 and R2).

R3 which is well beyond the margin zone and which currently exceeds 10 km must remain R3

Regarding R4 the speech is more difficult, it has completely cut the marginal area, but has not really extended to the central area, it has hardly moved since the opening of R3 and for this one I propose RC4 (rift candidate), but it can remain anonymous  and if necessary we can name it, for example, "marginal rift upstream of R3" and everyone will understand.

[paolo]

Baking,
1) Rift CR4 is the first to appear abruptly, but it almost stops after rift R3 opens, which absorbs the vast majority of the tensions.
2) Rift R3, after its emergence, has always had rapid growth and has just broken the point of resistance and reconnected with its extension forming a single rift.
3) The mode of formation of these rifts, their place of formation as well as their characteristics do not really correspond to the classical marginal fractures, but to the tensions caused downstream by the Cork
4) Before 2014 the formation of global rifts giving rise to calvings was mainly due to the extension of marginal rifts extending from the margin inwards (either on two sides or on one side depending on the situation of the shelf; classic modality, see for example K. E. Alley et al. 2019 )
5) Since and up to this moment (R1 and R2) we have switched to a "central rift" mode extending towards the margins forming from zones of fragility due to the formation of basal crevasses, transverse to the flow, created during the basic melting at the grounding line (see for example S. Jeong 2016).
6) The modalities of formation of global rifts therefore depend on factors that can change over time: pinning points that no longer exist, shear conditions that change, melting speed that varies over time (on this subject, for rifts forming at the centre it must be taken into account that they depend on grounding line melting and therefore on conditions that existed 7/9 years ago).
7) Currently, for the latest developments, we are, at least temporarily, in "rifts from the margins" mode.
Conclusion:
At the moment the existing conditions for the PIIS are very variable and we must not look at it in a fixed way, but follow carefully what is actually happening.

[baking]

This is worse. 

[paolo]

This is worse. 

What are you referring to?

[Stephan]

It must be unique and must not be changed over time.

I agree that we shouldn't change the numbering system. R0 (the thin new crack closer to the calving front) is a good idea to come along with.
We probably talk about days or weeks, not months - and then the cards are mixed newly after the soon-to-happen great calving event.

[baking]

I think the issue is we either have large scale images with lower resolution or nice high resolution images without any context, so we feel the need to say "Here is the latest picture of X."  The intent is to be helpful, but at some point it just becomes confusing and the casual observer will be turned off.

[blumenkraft]

We probably talk about days or weeks, not months

How about hours?

[blumenkraft]

I think the issue is we either have large scale images with lower resolution or nice high resolution images without any context, so we feel the need to say "Here is the latest picture of X."  The intent is to be helpful, but at some point it just becomes confusing and the casual observer will just be turned off.

I agree. This is why i proposed an easy to understand system.

[baking]

I think the issue is we either have large scale images with lower resolution or nice high resolution images without any context, so we feel the need to say "Here is the latest picture of X."  The intent is to be helpful, but at some point it just becomes confusing and the casual observer will just be turned off.

I agree. This is why i proposed an easy to understand system.

What about this part? "at some point it just becomes confusing and the casual observer will just be turned off"

[Stephan]

The latest Sentinel image shows the situation on 2020-01-06 at the western end of PIIS-MIS and on the eastern side the picture has been taken on 2019-12-27. Where these image match an estimation of flow speed is easy if identifiable features are visible on both sides of that "border".

I measured the speed at the R2 rift where both pictures are "matched". The southern rim moved ca. 150 m, whereas the northern rim had a shift of around 200 m. That means the rift R2 has further widened. The daily speed is calculated to 15 m/day, the soon-to-come iceberg moved by about 20 m/day. This movement of 200 m is constant through the northern part of the MIS until the calving front. These are higher values than measured ever before.
At R3 the values are: North rim moved by 150 m, the south rim by "only" 125 m, making this rift also wider, and revealing a speed of the MIS of 12.5 m/day even south of R3.
125 m is also the difference at the southern edge of PIIS-MIS where the zone of destruction begins.
Within the zone of destruction the shift is reduced to around 75-100 m.

At the southern end of the zone of destruction, where the slow Southern Ice Shelf begins, the pictures almost perfectly match (shift < 25 m), indicating that the positioning of the pictures is quite good.

[paolo]

It seems to me that we can close with the following proposition:
1) We keep R1, R2 and R3 as they are at the moment
2) No other rifts named at this time
3) As soon as a rift becomes important for the subsequent calvings, then it will be given the name (R4,..)

[blumenkraft]

What about this part? "at some point it just becomes confusing and the casual observer will just be turned off"

Well, the first one would be the number one. The second one number two and so on.

The ones from the margin would have a suffix.

I really don't think this is too confusing, even for a casual observer.

[Stephan]

the nothing that holds it all together

East of the Cork there is only about 700 m of ice left (measured from the new calving front to the western end of R2). How long will this "nothing" withstand the forces?

[oren]

How long? I am shocked it held until now.

[paolo]

mini-calving in the north
waiting for image of the south

[paolo]

won't get me so easily
I'm still here. Hee-hee. 

[paolo]

I had already prepared the images relating to the thicknesses of the "Ice rumble" west of the SWT deduced from two icebergs :
>> The first one, originating between the Ice rumble and the SWT, created in a calving between the 14/09 and the 27/09 and which turned over revealing a thickness of about 300m.
>> The second one, which was already detached on 14/09 but still in place, moved and turned over between 27/09 and 24/10 revealing a thickness of about 250m (it remained partially grounded in the new position to move definitively between 06/11 and 16/11).
But I hadn't finalized and mailed them.  I'm taking advantage of the peace before the storm to do so.

The thicknesses found are consistent with the thicknesses already published in a previous post and with the bathymetric data (also already posted).

PS: I don't have any examples related to SWT

Click twice to zoom and animate

Enclosed:
>> The animation with the two calvings
>> A zoom on the two icebergs


Translated with www.DeepL.com/Translator (free version)

[blumenkraft]

Calving. Still not the big one.

Link >> http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_202001/S1B_EW_GRDM_1SSH_20200108T041912_3F13_S_1.8bit.jp2

[grixm]

It also looks like there were some freshwater discharge on the other side, the water is blue like during mini-calvings:

[paolo]

Blumenkraft,
you are right to publish this image, given the poor quality of Modis images published yesterday, but given the exceptional moment with a day by day follow-up, when you publish an image from the previous day, to avoid any confusion, it is better to specify it 
(especially since the image has as name the date of today, even if it is an image of the 08; but it is true that both were made available today, PolarView is going off the rails at the moment ) ...

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[blumenkraft]

Oh, i thought it's from today! I was confused because it's not showing in today's Sentinel 3. But when this happened yesterday it makes sense. Thanks for the hint, Paolo.

[blumenkraft]

freshwater discharge

Makes sense. The whole shelf is really wet. Most extreme on the northern side and northern ice shelf. I was wondering if it's a freshwater discharge or calving debris.

[paolo]

Blumenkraft,
no matter,
attached today's image
PS : comparing the pictures of the 07th and the 09th it seems to me that it's more of a debris calving than a mini calving as I announced yesterday.

[paolo]

We were lucky no one created a "Poll: PIG next calving", we'd all have been ridiculed by the Cork.

[blumenkraft]

I bet so! I still can't believe it. It's unreal...

Is that cork-ice compressed and therefore stronger?

[paolo]

No, which was never opposed in rigid mode, but turning gave the MIS flow the means to move forward, while continuing to hold it in place.
The art of holding is to secundate the opponent, but there are limits to everything and now his game is at the end.

[Stephan]

I bet so! I still can't believe it. It's unreal...

Is that cork-ice compressed and therefore stronger?

I could imagine that this ice has been compressed. And maybe it also has become thicker last year due to the permanent pressure. Just look at the size the cork had one year ago. It was 25% wider (W↔E end in December 2018) than it was end December 2018 (SW ↔ NE end measured, because of its rotation).

[paolo]

Stephan, be careful, it's grown in the other direction, which means it's mostly deformed (to see it you must not take into account the pieces it has lost).

As I was saying below, always modify itself in order not to give in... (Cork's word)

And the Cork arrived at the test intact, with no old fractures that could have reopened and it did not suffer from shear or extension forces, but, for the most part, only from compression.

[baking]

We were lucky no one created a "Poll: PIG next calving", we'd all have been ridiculed by the Cork.

Go back and read our posts from November 19.

[paolo]

Baking,
but it wasn't a very firm prediction and it was made more to cool the spirits: "Calm down boys, it's not for tomorrow, we can't know when and it's not important to know". This post would therefore rather thwart a focus on forecasts.

excerpt from my post :
"…
I agree with Baking that it is the long term that is important and that the short term is only anecdotal
....
it seems clear to me that we do not have the means to make short-term forecasts.
That said, it's fun to make predictions:
1.   THE PIG/SWT joint could break in early December
...
5.   The iceberg detachment could be for February.
But I wouldn't play money on it"

Having said that, I did make some predictions, which, as you want to point out, turned out to be wrong.

[blumenkraft]

Having said that, I did make some predictions, which, as you want to point out, turned out to be wrong.

The prediction business is a bitch!

[paolo]

No Sentinel pictures today and Modis-Aqua shows us some beautiful clouds...
Time to finalize an old draft on the "Hudson Mountains" (NIS).

While reading an article I had discovered that there had been a recent eruption (210 BC) and therefore their volcanic nature.
In the site "Global Volcanism Program" I found :

* A list of known volcanoes in the Hudson Mountains (with name, coordinates and some related information) that I reproduced on a Modis image.
Remarks :
>> for the height of the "Maish Nunatak" there is a small problem, "Global Volcanism Program" indicates 232m but I found in an article the indication 310m (corresponding image attached), maybe the site refers to the height of the cone inside the nunatak) 
>> The Dean Nunataks are not on the list and I found their names elsewhere and the nunatak further north is practically a circle ...

* A summary of the information concerning them (and this is the maximum that can be found on the net) that I report below (the highlighting of the two eruptions is mine) :
"The Hudson Mountains, located along the Walgreen Coast in Antarctica's western Ellsworth Land, contain many only slightly eroded parasitic cones forming nunataks protruding above the Antarctic icecap.  The cinder cones apparently rest on three extensively eroded Miocene stratovolcanoes, Teeters Nunatak, Mount Moses, and Mount Manthe.  Subaerial basaltic lava flows dominate, but subglacial or subaqueous tuffs and lava flows are also present.  A tephra layer from an eruption of a subglacial volcano in the Hudson Mountains was dated from ice thickness at about 200 BCE.  The possible presence of steam was reported at one of the Hudson volcanoes during 1974.  Satellite data suggested that an eruption of Webber Nunatak took place during 1985, although this has not been confirmed". 

Also attached are three Sentinel 2 images of groups of volcanoes (named after their main volcano).  On these images I have also indicated :
>> two possible examples of subglacial volcanoes (this is not a thorough analysis, the structures on the surface may have any other origin or even be just an artifact in the images)
>> two examples of probable presence of volcanic ash on the surface (several origins being possible: outcrop following melting, deposition of melt water, ...)

In a following post you will find two zips containing zooms of some of these volcanoes and examples mentioned above.

In conclusion: I find this information interesting and that from a future not too far away, the melting of the ice above them progressing, these volcanoes could give signs of life (and they have already done so in the recent past).

Twice click to zoom in

Translated with www.DeepL.com/Translator (free version)

[paolo]

I can't attach zip files, I'll do it another way.

[paolo]

Enclosed are three images each containing 4 images

Twice click to zoom in

[blumenkraft]

Date     Name         UTC
Jan. 10   Wolf Moon   19:21

[baking]

I don't know if it is just the contrast, but today's low-resolution Sentinel-1 image shows all four major transverse rifts.

[paolo]

Three new animations based on the high definition images of the Sentinel 1 of 30/12/2019 and 11/01/2020 (not big news) :

Rifts on the NE side:
* R1 widening, but no extension
* R2: tension at NE with almost complete overshooting of the resistence point and joint between the two fractures and small NW extension before the resistence point (this extension partly absorbs the tension of the shelf and could temporarily block the extension at NE).
* R0 major extension and widening

Rifts on the SW side :
* R1 small extension : the very thin piece between R1 and R2 doesn't oppose any resistence it tends to follow the movement of R1 and widening.
* R2 major widening
* R3 impressive expansion and widening

Cork:
* tends to partially detach itself from the SIS and stick to the future SWT-SIS iceberg

Twice click to animate and zoom in

Translated with www.DeepL.com/Translator (free version)

[Andreas T]

pictures takn by Joanne Johnson, a geologist with BAS in the last few weeks show some of the Hudson mountains close up, taken at ground level. https://twitter.com/geologicalJo
there is a lot of very loose material which could erode and be blown onto the ice , dirty ice is shown in one of her images.



There is also a view of the northern corner of the PIG calving front seen from beyond Evans Knoll

dating rocks and glaciation is purpose of this expedition and the drilling planned for next year

[paolo]

Baking,
I think it's a mix: more contrast and wider rifts.

[Stephan]

paolo,
thank you a million for keeping us up to date. I still wonder how many days we need to wait before the big calving event happens...

[blumenkraft]

Any moment now...

[Stephan]

Any moment now...

I remember you writing that sentence weeks ago. It has been a very long moment so far...     

[blumenkraft]

Right! There is always a moment after that. We are not running out of moments. And only because the sentence is redundant doesn't mean it's invalid.