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Messages - nukefix

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Very scary picture of the collapsed NE Greenland 2000+ sqkm basin thats up to a km deep behind these Glaciers. On the right the dark area is inland of the coastal ranges. Now islands with the calving front merging all the glaciers from north and ne Greenland into one downsloping, below sealevel front, over 200 km long.
I have trouble understanding the point you're making - is the ice stream losing contact with some islands that currently provide back-pressure? I don't think the basin is "collapsing" at this point in time.

While Jakobshavn is already undergoing ice cliff failures and may very well undergo and temporary acceleration of ice cliff failures once the grounding line / calving front reaches the retrograde bed slope, but once that bed slope changes to a prograde slope then the temporary acceleration will stop and the ice cliff failures will slowdown to something like their current rate of calving. 
Is there evidence of such cliff failures at Jakobshavn? Do you have a link or a reference? I would imagine the calving front is getting quite a bit of lateral support from the channel walls which is holing the glacier back and preventing extra thinning and grounding-line retreat.

Is the grounding line (GL) close to the retrograde-part of the channel yet? My impression is that the GL is close or at the calving front in normal conditions. It's difficult to image the position of the GL from space at Jakobshaven but perhaps local cameras etc. are doing it in real time?

Greenland and Arctic Circle / Re: Greenland 2020 Melting Season
« on: July 31, 2020, 05:07:25 PM »
Arctic has seen a small scale coastal rock collapses. Similar but much larger scale events will happen when the rocks begin to melt further and further thus clearing pathway for ice to slide to sea.
The ice sheet in the area is grounded on bedrock that is rising, and that is already above sea-level, so there is no possibility of a marine-grounded ice-sheet collapse like in parts of WAIS.

Greenland and Arctic Circle / Re: Greenland 2020 Melting Season
« on: July 28, 2020, 10:55:33 AM »
This area interests SRS due to its broken geology that is also subsiding contrary to the rest of Greenland.
The area is question is NOT subsiding but is undergoing rapid uplift, see:

Sea-ice buttressing gone...a speedup of the glacier is probably taking place now.

Most beautiful satellite glitch <3
Looks like an orthorectification-error ... what is the source of that image?

edit: seems to be PolarView. I would guess that for some reason the geocoding of the image partially failed, as if they used an incorrect DEM, even though they don't use the DEM at all but only ellipsoid geocode  ???

Policy and solutions / Re: Tesla glory/failure
« on: November 08, 2019, 06:26:50 AM »
Surely the deployer of the AI technology, in this case Tesla, will be liable for any accidents it's software is causing? How does that affect the bottom line?
Musk has said repeatedly that under a Full Self Driving (FSD) scenario, the carmaker would be the responsible party when accidents occur, not the passengers. 
Ok, but isn't the situation in the US such that the amount of damages awarded in court is related to the ability of the defendant to pay them? In other words, individuals have been awarded payments in the tens of millions if big companies have been found to be at fault. Can this kind of litigation risk be insured away? Or am I just clueless about how the legal system works?

Policy and solutions / Re: Tesla glory/failure
« on: November 07, 2019, 09:49:26 PM »
Surely the deployer of the AI technology, in this case Tesla, will be liable for any accidents it's software is causing? How does that affect the bottom line?

More calving has taken place....waiting for higher-resolution Sentinel-1 IW acquisition.

Policy and solutions / Re: Tesla glory/failure
« on: October 10, 2019, 09:18:37 PM »
Where are the profits? Tesla shold be a business, not a religion.

It's October 1 (or later, depending on your longitude) and the most recent image I find for the Petermann Glacial Tongue is from September 29th.  PolarView image screen print below.  No convincing evidence the crack connects to the SW edge of the tongue.  The timing of the 'expected' calving event continues to elude us.
Now would be a good time to do InSAR-analysis of the tongue to see how far the crack really goes. It is not entirely straightforward since the tongue is moving between the image acquisitions. The data and tools to do it are free...if only I had the time..

Consequences / Re: Worst consequence of AGW
« on: October 03, 2019, 10:10:03 AM »

What is the original source of this graph?

Policy and solutions / Re: Tesla glory/failure
« on: September 24, 2019, 12:14:36 PM »
I think the autopilot must be crippled/disabled until it is crystal clear who pays the damages in the crashes that take place. IMO the deployer of the AI must pay - in Tesla's case that means Tesla.

Policy and solutions / Re: Tesla glory/failure
« on: September 23, 2019, 03:24:26 PM »
Shorties got nothing.
Where are the profits? If Tesla cannot generate profits, it does not matter that the cars are excellent.

Science / Re: Magnitude of future warming
« on: September 20, 2019, 11:25:41 AM »
I should add that even if we cut emissions to zero today, we have suppressed not just the next glaciation bu the next two.
How is that possible if CO2 sticks around only a few centuries?

Policy and solutions / Re: Tesla glory/failure
« on: September 19, 2019, 11:31:30 AM »
Beats Taycan .
The interwebs are going off over Porsche vrs Tesla.
That's indeed epic performance-wise. So far according to reviews the Model S has been described to drive like a muscle-sedan, not a sports-car. Traditionally Porsche has really excelled in the sportscar driving experience. I would imagin Taycan scoring high in this regard.

Regarding Tesla, where are the profits? The margins are going down as Model 3 cannibalises Model S sales, plus there are new viable competitors in the higher-end segment. This does NOT look good for Tesla.

Policy and solutions / Re: Tesla glory/failure
« on: September 17, 2019, 11:15:32 AM »
Where are the profits? Will there ever be any?

Antarctica / Re: PIG has calved
« on: September 16, 2019, 10:14:07 AM »
It is also possible to download Sentinel-1/2/3 data with the ESA SNAP toolbox:

Oh I did not realise it had only stopped to function in Chrome for me while it still works in Firefox - thanks!

Thanks John - where is the current landing/search page for the PolarView-data? The old site has been inactivated for awhile now...

1 gigaton of ice ~= 1km^3

The animations seem to disregard changes in local sea-level caused by global mean sea level rise, bedrock rebound and changes in the geoid. It would be super interesting to see simulations of those too..

NASA SVS has made these visualisations of simulated futures of Jakobshavn Isbrae until year 2300:

   [RCP 2.6]
  [RCP 4.5]
[RCP 8.5]

Super amazing!!

Policy and solutions / Re: Tesla glory/failure
« on: August 02, 2019, 01:22:11 PM »
Tesla makes very nice cars but it remains to be seen if it can be done in a profitable manner. BTW I think that Full Self Driving in the near future is a pipe dream.

Lakes of meltwater form on the surface of the glacier when there's a suitable surface depression that can contain the water. It does not imply there's a lake at the bottom of the ice sheet at the same location.

Glacial ice acts like a viscous fluid under pressure, not like a bunch of boulders. That being said there are channels that are enable meltwater to move towards lower pressure. I guess there could be some borehole studies of Jakobshavn but I haven't looked.

Jakobshavn does not appear to be floating but it calves very close or at the grounding-line.

So experimenting around with sentinel hub playground I discovered that although I could get the day, I couldn't figure out the precise image acquisition time...
That should be available here to the necessary degree:

The word of the street seems to be that not all scientists are fully convinced that marine cliff instability will play out as current models predict. It would help if it could be observed to happen in nature.


There is no change in the flow-path of the main trunk as it is confined to a narrow canyon. The "paths" plotted in the image are the flight-paths NASA did with their Airborne Topographic Mapper (ATM):

The Sentinel-1 images you posted are from ascending and descending orbits so their geometry differs. Also the presence of wet snow darkens the image by a great deal and I assume PolarView does some adaptive contrast stretching that complicated side-by-side comparisons when large contrast differences are present.

I still have no reason to believe salt water penetrates very far above the grounding zone but if you find a study arguing so I'd be delighted to read it!

Policy and solutions / Re: Becoming Vegan.
« on: May 05, 2019, 06:19:01 PM »
Unfermented soy is potentially harmful...better to use seitan etc. instead of tofu.

The GRACE satellite was an amazing tool from April 2002 until June 2017 & I look forward to seeing even better results from GRACE-FO:
Unfortunately there are serious problems on-board GRACE-FO, so the data-quality is likely to be a lot worse than for the original GRACE  :(

Antarctica / Re: PIG has calved
« on: May 04, 2019, 03:25:51 PM »
Also, what is your secret to getting such gorgeous images from SAR?  I assume your tool chain is SNAP and Gimp, but I'm struggling getting anything comparable.
Personally I like to view SAR data in SNAP using contrast stretched dB-scale. The steps to generate this are:
1) Use the calibrate-operator and calibrate the image into sigma0
2) In the calibrated image right-click on the sigma0-band and select 'linear to/from dB'
3) Adjust contrast stretching in the Colour Manipulation tool-window if needed. I find that the default 95% stretch works well in most cases.

my take is that it then took three years for sufficient seawater ingress to float the basal ice in the first trough and have that break through the overburden of glacial discharge.
The glacier is too thick to float and both GPR & seismic indicate it's solid ice until water-permeated glacial till at the bottom. The meltwater is fresh and it's being dumped into the fjord continuously. Can you find a scientific publication where the authors argue that the saltwater gets to penetrate upstream?

According to this paper:

...the salinity of the Subglacial discharge, Submarine meltwater and Basal Submarine meltwater is zero, which would not be possible if saline waters were penetrating into and under the ice-stream. Case closed?

Greenland and Arctic Circle / Re: What's new in Greenland?
« on: April 18, 2019, 01:01:10 PM »
ps: GRACE Follow-On - where are you? No info from NASA or Germany since late 2018. Is it in trouble as data was promised by now.
I heard that the accelerometer on one of the satellites is kaputt. That is not good at all and will quite drastically lower the data quality compared with fully functioning GRACE  :( :( :'(

Well, since (virtually) all rivers near coasts have salt wedges running up them as the tide comes in, I would expect similar tide-synchronised intrusions of denser salt water below the outflowing meltwater beneath the fragmented glacier by the cil.  Why wouldn't it?
I don't think the ice is fragmented as the pressure is around 100bar at 1km depth, but there are drainage channels. Tides increase back-pressure and can be detected far upstream but how far does the salt-water intrude? dunno

I found nothing in it that confirmed or challenged my view, apart from the step change of melange height above the cill [fig2] which, to me, suggests a deep logjam of melange, and if so then voids enough for tidal seawater/meltwater exchange.
johnm33 it's not "melange" but solid deforming ice all the way to the glacial till according to both seismic and ground penetrating radar studies. There is a changing network of glacial drainage but are there studies arguing seawater can be found upstream of the grounding-zone?

There is no water under Jakobshavn upstream from the grounding zone, which is very close to the calving front (part of the year they are at the same spot, so no floating tongue).

As far as I know there is zero evidence of sea-water penetration under Jakobshavn. Tides influence the back-pressure in the glacial plumbing system that should be full of glacial meltwater.

This thesis says

For this investigation I re-processed a 10 km-long high-resolution reflection seismic line at Jakobshavn Isbræ, Greenland, using an iterative velocity determination approach for optimizing sub-glacier imaging. The resultant line imaged a sub-glacier sediment layer ranging in thickness between 35 and 200 meters. I interpret three distinct seismic facies based on the geometry of the reflectors as a basal till layer, accreted sediments and re-worked till. The basal till and accreted sediments vary in thickness between 4 and 93 meters and are thought to be water-saturated actively-deforming sub-glacier sediments. A polarity reversal observed at one location along the ice-sediment interface suggests the presence of water saturated sediments or water ponding 2-4 m thick spanning approximately 240 m across.

A seismic image plus legend are attached.

this is why I formed the view that seawater penetration once past the first cill, at 5K, was more or less unstoppable, the more saline water will always pass over the inner cills and move upstream before it becomes dilute enough to move back towards Disko.
Above the grounding-zone (thai is close to the calving front in this case) the ice-stream is grounded, in other words not floating but sliding on bedrock/till. So your theory is that despite this there is sea-water penetration far inland? I guess that is possible and there are these deep blue icebergs coming out of Jakobshaven that could be a sign of ice made from freezing water (instead of compaction of snow).

The recorded calvings of giant icebergs I suspect are the result of the ice in the deepest part of the trough being floated and breaking through the weight of ice above freeing that space for seawater penetration.
No. If they were floating there would be a clear tidal signal there, and there isn't.

Is it correct to call it a grounding line if the ice is a composite of melange and seawater? if so ok.
The grounded ice is too thick to float, so no...

I think Espen means that the ice flow became noticeable after 2000, not because lack of coverage but because of actual changes.
Loss of buttressing sea-ice?

I can see from old satelite data that it started as a noticeable stream in the early 2000s, but you may have more to add?
Do you mean that before 2000 the satellite-data was so scarce the existence of the stream was not noticed from space? Today it's being mapped every 6 days by Sentinel-1...times have certainly changed  8)

So I'm guessing the build up of ice at the calving front is just a logjam of bergs waiting to be melted/lifted above the cill hence the pulsed release of bergs associated with tidal extremes.
AFAIK the grounding line of Jakobshavn is at the calving front, or very close to it. That would mean that the fjord waters are not penetrating under it. If they did, the tidal signal would be detectable far upstream from the calving front, and I don't think that is the case.

The following paper states:
We hypothesize that Jakobshavn Isbræ maintains a short floating tongue from winter to early summer, when ice flow exceeds ice loss by calving and the glacier front advances. In summer, iceberg calving surpasses ice flow, and the glacier front retreats, becoming nearly grounded by late summer.

I have long suspected that sea water has penetrated as far as the round feature upstream,
...not sure if there is any evidence of that:

There's also a feature midstream at the bottom of the image which is what I imagine a giant berg would look like moving in the stream.
The channel is full of ice upstream from from the grounding-line, so certainly in that position. Thick ice acts like a viscous fluid (like honey).

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