Mechanical erosion of ice sheets

[Iceberg]

Takening on the AR4 and ice sheet loss both greenland and antarctic.

The main reason for this is the consensus agreement required by the IPCC govt members, there is just too much uncertaincy as to what might happen, I'd say 80% of them think something will happen but that's not enough to start putting figures into the report. It would be too easy a shot for the anti's.

A shame really and one of the few negatives of the IPCC conservative method.

Going forward Our understanding of Icesheet's are really taking a quantum leap this decade though projects such as

www.ifremer.fr/ifrtp/pages/API%25202007-2008/API/130.pdf and the loss of Larsen B.

[Gray-Wolf]

The problem with Ross is sea temp increase. Seeing as a good proportion of the shelf is below sea level large areas of ice are exposed to the open Ross sea (the coastal strip is up to 4c above normal at the mo.). The undercutting that this allows (think Yorkshire coast here) leaves up to 200ft of ice hovering over nothing. The ice front is advancing so more ice is constantly being exposed to the 'warm' waters. The next IPCC document will include the ice sheets/shelves as areas of concern (and remain conservative).

[Iceberg]

New day, new evidence.

http://news.bbc.co.uk/1/hi/sci/tech/6364577.stm

Giant "blisters" containing water that rapidly expand and contract have been mapped beneath the Antarctic ice sheet.

The results, published in the journal Science, show that some areas fell by up to 9m (30ft) over just two years.

"We didn't realise that the water under these ice streams was moving in such large quantities, and on such short time scales," said Dr Helen Fricker of the Scripps Institution of Oceanography, University of California, and one of the authors of the paper.

"We thought these changes took place over years and decades, but we are seeing large changes over months."

The results are important for understanding how the Antarctic Ice sheet, which contains nearly 90% of the world's ice, may respond to global warming and how much it may contribute to sea level rise.

I wonder what happens when these rivers grow by a) increase speed of ice movement and B) greater warming ?

Maybe a Larsen mark 2.

Finally http://www.igsoc.org/journal/53/180/

If you've got a bit of spare money or just want access to the latest papers a very good site.

Matt

[Gray-Wolf]

Thanks for that Matt!

I do feel that, protected by the ice cover, the base of Ross is not that well protected and ,seeing as the sea is 'warm ' by comparison , basal assault can only compound the problem.

Seeing as the ice sheet is 'dynamic' then it becomes riddled with multiple fractures/crevasses/faults and so there are plenty of areas for water to 'inhabit' in a fluid (supercooled and under pressure) state.

Water under pressure is a mighty force (for anyone who has accidentally 'jet washed' mortar from joints knows!) and ,as the title of the thread suggests, the rapidity of 'ice dam' collapses at the end of the last ice age is well documented in both scale and impact. Though not unexpected I hate it when things I worry about turn out to be other than 'paranoia' on my part.......I'd rather be paranoid than have the world under the threats I 'perceive'.

Ian.

Sorry Matt, Replied before reading the article! So the area is part of the system feeding Ross and no-one could understand my concerns about possible cold water outflow this southern summer (NZ anomalies). I wonder if we have a mechanism for this phenomena now?

Edited February 16, 2007 by Gray-Wolf

[Gray-Wolf]

Bleedin' Edit feature....couldn't it at least wait 'till 2 posts on?

To have 'witnessed' this mechanism working at 'superfast rates' makes me wonder how widespread a phenomenon this is.

Can you imagine the Hydrolic pressure needed to lift 1,000ft of ice 30'? Can you imagine what happens in areas where the waters passage isn't 'blocked' and so flows normally?

In the normal course of events the water will exploit cracks and fissures (melting them as it goes) to travel. Only when dammed would we expect the water to 'back up' and for this feature to dam for 2 yrs it must HAVE been quite a blockage but obviously no more!

The ice streams that exit under Ross widen channels which the 'warm' sea water can then exploit undercutting the base which, in turn, must lead to collapse/slumping of the ice sheet above.

As I observed the IPCC will have Rapid ice melt in the Antarctic in there next report and some very worrying sea level predictions too I guess........

[Gray-Wolf]

It would seem that the 'real time' effects of climate change generate little interest whereas debating the possibilities do! How queer.

Apparently the NASA report focuses on the WAIS and it's drainage out through the Ross Sea and studies of the 'outflow' are ongoing. If anyone could help track down this research I'd be grateful. Ted Scambos is the Joe doing the work but I'm struggling to find him/it.

The ice dam parallels are now easier to appreciate and it would appear science has given a resounding 'Yes' to my original question of the mechanical erosion of the ice sheets acting very much like ice dam failures.

Edited February 16, 2007 by Gray-Wolf

[Iceberg]

I am still trying to find more about it GW, like you.

It seems like everything else in Nature, these large icesheets are very fragile, you get the feeling that they can stand a few years of increase warming or increased precip through a stronger South polar Jet, but can they withstand 10-20 years of this in a row........

[Gray-Wolf]

I tend towards viewing us as already being 20yrs into this (LarsonB and B15 from 'The Ross' were not minor first rumblings surely?) which is why I am so keen on things. There is half a continent of ice being 'held back' by Ross's grip on the seabed and either undercutting/slumping or the pressure from behind will shatter it and unleash one heck of an outflow.

The basal erosion is isolated/insulated from the climate above and so continues (under it's own steam as it were) 12 months a year (unlike the summer melt).

[Iceberg]

It does seem like a bit of a slippery slop (no pun intended !).

Increase slippage of the Major iceflow into Ross increases stress leading to more cracking and fractures.

Increase basel slippage of Ross and it's protective areas.

Increase meltwater on the surface of Ross leading to more drainage down the increasing cracking and fractures.

More weakening etc.

The only thing that's really going to reverse it is a decade or so of less precip and less summer melting (like that's going to happen), and in the meantime things will only get worse, still up in the air though what worse is.

Matt

[Gray-Wolf]

So long as it isn't large sections of the ice sheet that are 'up in the air'.

From my knowledge of Mine collapses any 'collapse will 'heal' within 7 times the height of the collapse, i.e. the jumble of rubble on top holds up the surface. This means that many of the ice streams could have carved out huge caverns that only ground penetrating radar/siesmic studies would show. Not many folk trogging around WAIS doing just that at the moment.

[parmenides3]

Ted Scambos is 'ere: http://nsidc.org/

William Connolley is also a possible source: http://scienceblogs.com/stoat/

I'm still cautious about the timescale you're suggesting, G-W, if only because you are out on a limb in relation to the scientists who are doing the research. I've got an interesting paper (if I can find it) which I'll post later.

:)P

Edited February 16, 2007 by parmenides3

[Gray-Wolf]

Ted Scambos is 'ere: http://nsidc.org/

William Connolley is also a possible source: http://scienceblogs.com/stoat/

I'm still cautious about the timescale you're suggesting, G-W, if only because you are out on a limb in relation to the scientists who are doing the research. I've got an interesting paper (if I can find it) which I'll post later.

P

Ta muchly P3!

[parmenides3]

If you like those, you'll love this: http://igloo.gsfc.nasa.gov/wais/pastmeetings/Sched06.htm

Also, check out the 'West Antarctic Ice Sheet Initiative'; googling should get you there.

:)P

[Gray-Wolf]

I'm up to my neck in pooh at the mo. but I'll get round to it later, thanks again (My article hound hero!)

[parmenides3]

I'm up to my neck in pooh at the mo. but I'll get round to it later, thanks again (My article hound hero!)

Been one of those days, heh?

[Gray-Wolf]

Been one of those days, heh?

Week more like !, if I hadn't taken the time to abuse my stomach so much in my past I'd be poorly too but oh no, 'been there done that' says my imune system so I'm left to pick up all the 'dropped' jobs whilst they have a jolly time being 'poorly'........Pah!!!

[parmenides3]

I'm sure there's no real comparison, but we do have two ageing incontinent cats with bad aim, so I can at least sympathise. I won't tell you about my teeth, though.

:)P

[Gray-Wolf]

I'm sure there's no real comparison, but we do have two ageing incontinent cats with bad aim, so I can at least sympathise. I won't tell you about my teeth, though.

P

As long as it isn't an upper left Wisdom tooth I don't wanna know!!! Why can't we have sharks dentition? push 'em out and drop in a new one????

Edited February 16, 2007 by Gray-Wolf

[parmenides3]

I'd settle for BUPA dentition... :(P

[Gray-Wolf]

Well that's another week blighted by fog banks and low cloud! I wish I had access to some cloud penetrating terrain images of the 250m resolution!

The odd 'glimpses' of sections of the crevasse, from various angles/sunlight angles, make me just wonder at the dimensions we are talking about here.

It must be 10's of metres across and ,by the shadows it has inside it, quite deep now as this years snow cover melts back.

After reading some more papers on glacial calving into the Ocean it seems that once the ocean 'lifts up' the front edge of the ice shelf then the leading edge of the shelf will break off as far back as the first piece of ice attached to the seabed.

If there is a natural 'break point' in the shelf then I reckon it'd fail there.

Lets see what the first of the Autumn storms do to the front edge of Ross this March!

Edited February 22, 2007 by Gray-Wolf

[Gray-Wolf]

Seeing as it 'wouldn't do' to 'pollute Mondy's thread I'll froth here instead!!!

Ask any Inuit who still makes tempory shelters from Ice/snow whether it makes pretty good insulation from the 'outside' or whether they just make igloo's as a 'chill room'!!!!

Ask any miner what temperature does with depth (1c per 1000ft) and you'll see that a mile of ice will creat some unique conditions at depth.

Ask all the critters that swim under the ice shelf/sheets over winter whether it is -40c down there or not!!!

Warmer oceans lead to;

Increased basal melting of ice sheets/shelfs,

Increased storm frequency/intensity leading to extra 'dynamics' across the ice (it breaks if you wiggle it too much).

Increased precipitation in the 'desert' that is antarctica

'Warmer airmasses' penetrating further into the 'fringes' of antarctica.

try and 'think' about these things and challenge the science if you must but please keep sillyness to the 'life ,the universe.......' thread!!!

Edited February 24, 2007 by Gray-Wolf

[Gray-Wolf]

Part of the suite of cracks running out from the edge of Roosevelt Island were visible today along with the remnant of the B15 calve (the one 'wired for sound').

You cannot help but note a similarity the dimensions of these cracks when you compare them side by side, the only difference being you can see the sea through the end of the B15 remnant (the 200ft cliffs there are split through to the base) so you have to wonder if, pre the B15 calving event it didn't present a similar set of fissures at the surface. Time to hunt down the 2002 feb archives from Modis methinks........

I'll try and master 'cropping' the images from todays overflight so you can see for yourselves whether they are similar or not. If I fall lucky and get the Feb 2002 images I'll post them up too!

[Gray-Wolf]

This is a Dec image of the area I'm interested in. The top left corner shows the remnant left by the B15 calve in 2002( the jutty out bit) Remember these cliffs (where ice meets sea) are up to 200ft high.

here is a closer view of the remnant. Notice the 'crack' and remember, the hole at the east end of the crack goes down 200ft to the sea below!!!

Here is 'my' crevasse today. Note how 'similar' the crack looks to the unexposed crack on the B15 remnant.

Above is the Calving of B15 in march 2002. Remnant B15 is now centre right of the picture and upside down compared to the other images above.

Notice that it's size is comparable with the 'slab' my crevasse marks out. If there is a mechanical reason for failure 'X' metres from the edge of the shelf then this 'slab ' will fail (it's already as advanced as the 'crack 'on the B15 remnant).

Edited February 25, 2007 by Gray-Wolf

[Gray-Wolf]

Robin Bell & Michael Studinger of the Lamont-Doherty Earth Observatory are sounding like they agree with my alarm at sub-glacial erosion. they have found some 'alarming' discharges from the East Antarctic Ice Sheet (not the beloved WAIS) .35Billion tonnes of ice into the Weddal sea annually, the 'Recovery' Ice stream draining an area of 8% of the E.A.I.S. is also concerning them greatly.

The say " until about a year ago, not many people cared much about sub-glacial lakes, that's changing, but we're still only just beggining to understand how these lakes ,sealed beneath more than two miles of ice, have the potential to impact the rest of the world"

I thought I wasn't as mad as all that!!!

Edited February 26, 2007 by Gray-Wolf

[parmenides3]

G-W; there's no argument about your underlying concerns with the stability of the WAIS; it's the whole issue of timing and forcing which is the key question here, I'm sure you'll agree.

I'm happy to see your pics and references as the 'early warning signs' they are, but how early, and how far down the line, is the nub. You say 'imminent', I say 'eventually', though neither of us can put a definitive number on it, because of the lack of data. I think your research is useful though, bringing together a variety of pieces of evidence. As it's International Polar Year, I'd expect a lot of new material to become available in the coming months. it may be that we'll be in a better position to 'read the signs' then.

Keep up the good work.

:)P