Mechanical erosion of ice sheets

[Gray-Wolf]

In Case you can't be bothered to look here is a cropped image from the middle of the Ross sea ice mass taken yesterday A.M.

[Gray-Wolf]

And just to triple post I'll outline a mechanism that could cause this type of failure across the Antarctic.

We know that sea ice thickness has been diminishing over the last 15yrs and that ,as the amount of 'multiyear ice lessens , the proportion of sea ice that is single year ice increases.

Obviously the integrity of thin ice isn't as great as that of multi year ice.

When I posted around Aug 28th that we may just 'have turned the corner' with the ice extent in the south, and was warned by P3 that it was mighty early for it to 'max out', I was a little gutted to then see the ice extent growing at an alarming rate. It didn't make sense to me at all (nor did I think the conditions down there conducive to rapid ice build) but 'facts are facts' aren't they?

When I looked at the images from around the southern continent yesterday to find that all visible sea areas were in similar states of disruption I was alarmed at what I saw.

I just couldn't figure what could do that all around Antarctica (in a similar time frame as all the ice looks to be broken in a similar way with no visible 're-freeze of fractures). A storm may surge and break apart one area but not the opposing side of the continent surely? Then I thought about the impact of a 'high tide' especially the 'spring tides'....I then looked back at the 28th Aug and found it was a full moon on that date (highest tides?) and that it was near the equinocturnal high tide too so a pretty big tide to boot!

I propose that the integrity of the southern sea ice was so low that the tides around the last full moon buckled and fractured the pack leading to it 'ease apart' and fooling the 'ice extent' imagers into thinking it was ice growth. It is only the increase in daylight down there that now makes visual inspection possible.

Watch this space???

[Gray-Wolf]

Four poster? I'm turning into a Bed !!!

I'm Gonna fire of an E-mail to Robert Grumbine (U.S. Antarctic survey at McMurdo) as he was kind enough to help out last year with my queries about the 'crack' even though his expertise is sea ice.

Seeing as this time I'm asking on his specialist subject I hope to get an even fuller reply!

[Gray-Wolf]

Note to self. Robert Grumbine of the U.S. Antarctic survey team is now in receipt of my E-mail seeking his interpretation of my observations. Now I'll see if I'm going crazy!

[Iceberg]

Where these cracks there this time last year ?, i.e do the appear every year and then glossed over by snow and frozen melt during the summer months.?.

Certainly interesting, hope he replies quickly.

High res AMSR + scan of the region.

Edited September 19, 2007 by Iceberg

[Gray-Wolf]

Where these cracks there this time last year ?, i.e do the appear every year and then glossed over by snow and frozen melt during the summer months.?.

Certainly interesting, hope he replies quickly.

High res AMSR + scan of the region.

The cracks on the shelf front have been there a number of years, over the last 2yrs the have appeared to extend and widen (hence my concern! The 'cracks' are the remnant crevasses from when the glaciers that form the shelf either went over an obstacle or down a steep incline (a slo mo waterfall!). When the glacier 'flattens out again the cracks push back together but the inherent weakness remains. You need also bare in mind that the cliff at the edge of Ross ice shelf are up to 200ft high so it'll have to be a very deep fissure to fail.

here's another take on todays anoms and as you can see The Ross sea melts from the inside out.By November there will be a warm water plume flowing out past Mcmurdo into the Ross sea.

As for the smashed up /shattered appearance of the sea ice around Antarctica, I do not recall seeing it last year and , in fact, most of the coast/shelves held onto portions of their 'winter ice until early Jan. Apparently not this year !

We'll see how Mr Grumbine responds to my questions to discover how 'normal' a process it is!

If you see on your image at the Mcmurdo/Mt Doom end of things that this years melt/outflow is already developing.

Edited September 19, 2007 by Gray-Wolf

[Gray-Wolf]

One of yesterdays views showing a large chunk of the far end of Weddell in collapse

Here is Cyprus at the same resolution

As you can see the area of collapse is quite large. If you save, and then view in your browser, you can see the disruption to the sea ice around the collapse showing us it is a recent event. Later in the season this 'chunk' will itself start to be broken up further/drift into deeper waters and be broken up further.

All in all an early start to the season.

[Gray-Wolf]

http://www.sciencedaily.com/releases/2007/...70920122154.htm

Talk about mixed signals! I am no longer listening to the 'cooling Antarctic' Paff. There may well be regional variations to temps but there is only ONE trend and that is towards ablation.

Of course most of it seems to be across my patch ( the meltwaters perculating to the base increasing both pressures and lubrication.....as in ice dams?)

Edited September 22, 2007 by Gray-Wolf

[Filski]

i was wondering if you'd spotted that article

Here's another I just came across, a little old. I hadn't thought about the possibility of earthquakes fracturing the ice sheet before.

[Gray-Wolf]

i was wondering if you'd spotted that article

Here's another I just came across, a little old. I hadn't thought about the possibility of earthquakes fracturing the ice sheet before.

You need to try and post the link again please!

If you remember that Mt. Erebus (with it's permanent Lava Lake) is at the western end of Ross (just north of Mcmurdo) you'll see how 'active' an area this is. There are also regions of volcanic activity , and heat loss, under areas of central Antarctica which may help with the sub ice lakes and streams and provide the means for the mechanical fracturing of the base of the sheets.

The current state of Ross ice shelf (and it's potential for catastrophic collapse) must be under renewed scrutiny after NASA's snow melt revelations as it provides one of the 2 main features that were witnessed before Larsen B collapsed in 2002 (the other being 'melt water pooling' on top of the shelf....... watch this space!!).

[parmenides3]

Just to say keep up the good work, G-W; even if I don't write often, your thread is still one I check out regularly. We'll be entering the melt season soon, but for the Ross I'd recommend keeping and eye on King George VI glacier and Pine Island/Thwaites, as well as watching the thermometer and the ozone hole. If recent research is right, this last could be an important factor (three times more so than global mean temps) in inducing or suppressing Summer melt.

:)P

[Gray-Wolf]

Hi P3!

This is a screen grab of the NASA snow melt findings from back in 2005 and you can see what was happening just around the corner from Ross (EAST) in the Pine Island area (if I've got my areas correct!!!)

So you can gauge how important the melt water pools/perculation through the Glacier to the base is!

Up on the Autumn thread I'm posting images of the melt (cloud/Fog willing) and some areas (60E to 90E, Peninsula, Ross sea) seem to be quite advanced already.

I'm hoping this year to be able to post the melt water pooling I believe I'm seeing at the rear of Ross (at the base of the fringing mountains) now NASA has published it's 20yr snow melt maps (and I no longer feel too 'extreme' in my interpretations!).

Thanks for the encouragement, every little helps (as those b* stard planet killers are keen to remind us!!!).

[Filski]

Oops

http://www.guardian.co.uk/environment/2007...8/climatechange

[Gray-Wolf]

Thanks for that Filski!

The sudden 'offloading' of catastrophic collapses must make you wonder about the process of isostatic uplift and it's effects on already existing fault surfaces. In the 'old ' models uplift is a very slow process (as is still being witnessed today in Scotland with the 'raised beaches' around the Lochs/Coast but maybe, on a local scale, the removal of such loads 'instantly (in geological timescales) may lead to the re-activation of long inactive faults. The Breakup of the ice itself also promotes 'mini-quakes on the ice surface and , in Greenland at least, many of these are being witnessed.

In line with the thread title this begs the question of whether these 'mini quakes' provide us with information of the basal erosion of the sheet and the possibility of 'caverns collapsing at the base' (these would infill with their own ice rubble within 10 times the height of the cavern so would not appear at the surface but would fundamentally weaken the ice sheet) causing the tremors.

[Gray-Wolf]

My first 'clear image ' of my crack this year. I for one am quite surprised that this seasons snow/drifted snow appears to have had little impact on the appearance of the thing (I thought it would have filled in with snow blowing towards the coast on the Antarctic continental winds but no!)

and here's Northern Scotland at the same scale/resolution......

[parmenides3]

I'm glad it's you who's making this post and not Lady P ! (blush).

:)P

[Gray-Wolf]

I'm glad it's you who's making this post and not Lady P ! (blush).

P

Well, it was nice knowing you P3! ......now I'm off to split on you!

[Gray-Wolf]

My crack must've gotten lonely over winter and majicked up a few pals!!! I was surprised to find my crack so snow free so early when I posted the first of the years images so to find other crevasses opening up (and slumping the snow above) is definately a worry.

Meanwhile up the coast the B.A.S. boys are concerned at the recent calve off Pine Island....just wait 'till they see whats happened further down in East Getz!!

Promises to be a 'happening' summer down there!