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Author Topic: WAIS / EAIS eventual collapse question: huge tsunamies possible?  (Read 2035 times)

F.Tnioli

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This question, i am pondering upon for years already. And it's yet far from getting any definitive answer to it.

While most concerned citizens around are primarily concerned about how _high_ sea level can rise then or then, me - i'm most concerned about _how_ sea level will rise. Personally, i doubt it'd be slow and steady all the way through.

I'd be grateful for any reasonable thoughts, estimations, geological data (such exceedingly powerful tsunamies had to happen in the past already, at very least after big asteroid impacts, so there has to be some geological evidence left).

In particular, i am most interested to learn about any modelling of effects produced by catastrophic-scale tsunamies which would produce wave over 100 meters high by the time it hits shores. I suspect such modelling was done by some few groups related to asteroid impacts (ones in the past, based on geological evidence - and/or pure modelling for possible future impacts). Yet, i didn't happen to find any detailed research of the sort, so far.

How far tsunamies of this kind of size can go through oceans? How far 100+ meters high tsunami wave would travel on "nearly level" land? How dangerous secondary and tertiary "reflected" waves would be? Will such tsunami waves would still be practically safe for ships which are far enough from any land, or not quite? Etc.

P.S. If you think the answer to all this is "definite NO, that can't happen", then please at least read this recent publication in its entirety and also this one, too. If after reading those you're still sure "definite NO", then please let me know why. I'd like to hear every possible opinion.

P.P.S. I know this matter is not about "tomorrow", "this year" or "this decade", for that matter. Most would say not even "this century" for EAIS case, i bet. But, i'm sure noone would be hurt if we'd learn things about such processes "a bit early". Besides, noone can really know if it's "way too early" to talk about it or not, because we have no idea what it'd take to dodge this kind of bullet for our globalized industrial civilization, which grows increasingly more dependant on regular, intensive and reliable intercontinental trade, most of which is done with ships and ports all around the globe.


oren

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #1 on: July 05, 2017, 10:28:24 PM »
F. Tnioli, I recommend to read the Wiki article on mega-tsunamis to begin with.
https://en.m.wikipedia.org/wiki/Megatsunami

Personally I don't think a WAIS collapse event can trigger a significant mega-tsunami, but I haven't done any math or research.

RikW

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #2 on: July 06, 2017, 08:55:20 AM »
I doubt this could happen. I think the sea isn't deep enough to cause a mega-tsunami and I doubt the impactspeed of such a major calving even will be too slow.

steve s

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #3 on: July 06, 2017, 09:25:25 AM »
Limitations on ice cliff height due to ice strength put an upper bound on possible energy delivery from a calving event. An ice dam collapse scenario can generate high forces in a channel due to gravity, which are the scenarios generating erosion features and depositing rocks at great heights (Missoula Floods, for example) but do not have much influence in open water.

Also consider that with any Antarctic event the wave front would expand over the long ocean distances, diminishing the impact on other continents.

I see no mechanism through which melting could generate much of an intercontinental tsunami. 

VaughnAn

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #4 on: July 07, 2017, 12:09:20 AM »
Scientific American Magazine published an article on this possible scenario in circa 1993-1995.  The main thing I remember was that they considered a mega tsunami possible but of low probability in 200 to 300 years.  Since we have come about 200 years(my guesstimate) in climate change years in the past 25 years maybe this is eventually a possibility???

I have not been able to find this article so if is around I would like to re-read it. 

F.Tnioli

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #5 on: July 07, 2017, 12:23:59 PM »
F. Tnioli, I recommend to read the Wiki article on mega-tsunamis to begin with.
https://en.m.wikipedia.org/wiki/Megatsunami

Personally I don't think a WAIS collapse event can trigger a significant mega-tsunami, but I haven't done any math or research.
Thanks for the link. I knew most of what the article has, but surprisingly in this case Wikipedia has much more info on the subject than one would expect from any wikipedia article.

I notice you only voiced your opinion about WAIS case. What about EAIS?

F.Tnioli

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #6 on: July 07, 2017, 12:32:36 PM »
I doubt this could happen. I think the sea isn't deep enough to cause a mega-tsunami and I doubt the impactspeed of such a major calving even will be too slow.
I see.

However, like mentioned in the Wikipedia article Oren mentioned, quotes:

"The asteroid linked to the extinction of dinosaurs, which created the Chicxulub crater in Yucatán approximately 66 million years ago, would have caused an over 100 metres (330 ft) tall megatsunami. The height of the tsunami was limited due to relatively shallow sea in the area of the impact; in deep sea it would be 4.6 kilometres (2.9 mi) tall".

"The large mass of rock, acted as a monolith (thus resembling high-angle asteroid impact), struck with great force the sediments at bottom of Gilbert Inlet at the head of the bay. The impact created a large crater and displaced and folded recent and Tertiary deposits and sedimentary layers to an unknown depth. The displaced water and the displacement and folding of the sediments broke and uplifted 1,300 feet of ice along the entire front of the Lituya Glacier at the north end of Gilbert Inlet. Also, the impact and the sediment displacement by the rockfall resulted in an air bubble and in water splashing action that reached the 1,720 foot (524 m.) elevation on the other side of the head of Gilbert Inlet".

Those cases demonstrate that no "deep" sea is required for mega-tsunami of the wave size i mentioned in the 1st post of this topic to form: sediments are part of the process, and wave heights of the 100 meters magnitude and higher are still the case.

Another thing - who said it must be "calving"? Personally, i also doubt any "calving" event would produce a megatsunami. Other mechanisms are my "suspects" here:

1st, cascade structural failure of large body of ice, caused and triggered by ongoing (as we speak) weakening of the bottom parts of ice sheet(s), which is being melted by ocean water "from below", which is what one of links i gave in the 1st post is exactly about, and my primary concern for WAIS; and

2nd, possible "ice dam failure" event of gigantic proportions, resulting in _billions_ to _trillions_ of tons of ice and water flowing "down" from upper elevations all the way into the ocean, which is what the other link in the 1st post is about, and which is my primary concern (eventually) for EAIS.
« Last Edit: July 07, 2017, 12:39:49 PM by F.Tnioli »

RikW

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #7 on: July 07, 2017, 05:11:23 PM »
It's just my gut feeling, but I'd say a tsunami is formed when enough water is displaced fast enough. And for a mega tsunami it should just be more water being displaced faster.
I can't imagine that happening on antarctica.

The 2nd situation I think will trigger rapid sea lvl rise, but not a mega tsunami. I can imagine that to happen (though not creating a mega tsunami)

steve s

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #8 on: July 07, 2017, 05:59:46 PM »

1st, cascade structural failure of large body of ice, caused and triggered by ongoing (as we speak) weakening of the bottom parts of ice sheet(s), which is being melted by ocean water "from below", which is what one of links i gave in the 1st post is exactly about, and my primary concern for WAIS; and

2nd, possible "ice dam failure" event of gigantic proportions, resulting in _billions_ to _trillions_ of tons of ice and water flowing "down" from upper elevations all the way into the ocean, which is what the other link in the 1st post is about, and which is my primary concern (eventually) for EAIS.


The first fails on the basis of speed of propagation. Ice flexes and stretches. Then it has to travel to where it could displace water.

The second fails for two reasons. First because the antarctic has little suitable terrain:


Second because the wave front spreads out as it covers intercontinental distances. The mega-tsunami article does not mention major intercontinental impacts, other than leaving the possibility open for extraterrestrially-generated events.

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #9 on: July 07, 2017, 06:01:00 PM »
The first attached image shows a cartoon of the 1958 Lituya Bay megatsunami (landslide into a bay).  Just image what impact an ice calving "cliff failure" within the confines of the Byrd Subglacial Basin in the WAIS would have w.r.t. to a local megatsunami hitting the adjoining ice cliff faces:

http://wikivisually.com/wiki/Megatsunami


Edit: the second image shows the geothermal heat pattern within the Byrd Subglacial Basin & the third image shows some of the water depths beneath the Thwaites Glacier
« Last Edit: July 07, 2017, 06:14:36 PM by AbruptSLR »
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F.Tnioli

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #10 on: July 10, 2017, 03:00:57 PM »

1st, cascade structural failure of large body of ice, caused and triggered by ongoing (as we speak) weakening of the bottom parts of ice sheet(s), which is being melted by ocean water "from below", which is what one of links i gave in the 1st post is exactly about, and my primary concern for WAIS; and
...

The first fails on the basis of speed of propagation. Ice flexes and stretches. Then it has to travel to where it could displace water.
...
Can't agree. Ice breaks and fractures much more often than it flexes and stretches. Under "cascade failure" term i meant the situation when any big mass of ice which at some point is being supported by couple columns of lower-elevation ice - eventually drops down as a result of said columns' thinning (melting) under gravity, and that drop of a big mass of ice causes further (lower elevation) masses of ice to break and fracture, following further down with ever increasing force and velocity.

Much like an avalanche.

As for "it has to travel where it can displace water" - how about travelling directly down into partially-liquid-water WAIS basin? Quotes from the article linked 1st in 1st post of this topic (my bold):

"... the West Antarctic Ice Sheet, which is up to two and a half miles thick and covers an area twice the size of Texas. The ice sheet is draped over a series of islands, but most of it rests on the floor of a basin that dips more than 5,000 feet below sea level",

"... And at depths of 2,000 to 3,000 feet, along a seafloor canyon that ran straight under the ice, warmer seawater was streaming in.",

"... the ice shelf was losing 13 cubic miles of ice per year from its underside;",

"The sub’s sonar data, meanwhile, revealed the breathtaking landscape it had navigated. The bottom of the ice shelf was corrugated with not just one but many channels, which cut as far as 600 feet up into it. The walls of these inverted ice canyons were sculpted into terraces, ledges, and sharp corners, and along the ceiling of each ran a gaping crack that penetrated even farther into the ice".

It is therefore only a matter of time until WAIS itself - considering how much below sea level big part of it is located, - would be losing dozens and later hundreds cubic miles of ice per year from its underside, and in my opinion, that will surely create some cascade failures when parts of its upperside would crash right down when underside is too much "swiss cheeze".

The only question, to me, is what sort of scale such events will be near then-current edges of remaining WAIS, the latter being a requirement for any significant tsunami wave to form, of course.

DoomInTheUK

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #11 on: July 10, 2017, 04:36:55 PM »
FT.

A tsunami needs to move the whole column of water, otherwise it's just a big wave. If the top part of the ice breaks off the underwater part becomes unstable and breaks off, but upwards. It'll be turbulent, and I wouldn't want to be anywhere near it when it went, but it'll be a localised wave.

Worry more about the side of a Canary Island volcano collapsing into the sea. This would cause a Tsunami, and a big one at that!

Ice just won't be able to move the whole water column.

F.Tnioli

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #12 on: July 12, 2017, 02:16:16 PM »
Would you kindly not tell me what specifically to worry about, DoomInTheUK, because if you do, then i am forced to reserve the right to respond in kind, with something like "worry about something else than this topic". It won't end well, so let's not start with it. Deal? ;)

To the subject. I know what you mean, but i used the "tsunami" word for simplicity. Thing is, when "just a big wave" gets big enough, its effects can and will approximate those of "proper" tsunami wave rather well.

Next, i certainly didn't mean underwater part of ice being responsible for forming up the wave. Therefore your argument about it, while true in itself, - is irrelevant to what i was talking about. For the record, "cascade failure" i meant was all about above-water parts of WAIS (in the future, after WAIS loses most/all shelves and will be melting in its core parts).

One can see both such "cascade failure" (only partial and limited, though) and also resulting water wave of many meters height - in about 1 minute here.

Note that the above video evidence is produced by calving of mere thousands of tons (from the looks of it) of ice which drops down to sea level from mere several dozens meters height (from the looks of it). Imagine what will happen if we'll have trillions tons of ice dropping down to sea level from many hundreds / couple thousands meters elevation. The mere mass and inertia of the fall could easily move whole water column as you "request", even produce a crater in the seafloor if it's shallow enough waters under the collapsing part of the WAIS (and there are plenty of locations).

At more deep water locations, it might not move the _whole_ water column, but it'd still be a wave of unprecedented proportions if large enough portion of WAIS fails structurally and drops down, crashing through all the openings and "caves" created by underside melt, as described above.

And if anyone doubts whether trillion-ton scale fracturing is possible, - quite "conviniently", an iceberg more than 1 trillion ton in mass separated from Larcen C just today, i heard elsewhere; this is probably already reported in some nearby topics. So you see, even floating parts can fracture at this scale - means, to me, that parts which are "anchored" and have much of their ice weight being supported by solid ice structure and ultimately bedrock, - those parts will possibly fracture at even much bigger scale "momentarily", as soon as underside melt corrodes supporting solid ice structure sufficiently.

It might end up being thousands of trillions tons of ice dropping down at some point in a single event. The sort of wave created out of such event may not have appropriate term in english yet - it's not exactly "tsunami" and it's too big to just be referred as "just a big wave locally" (like the one in the video linked above), but do we really need to stay blind to this future danger only because we don't yet have common established term for such events?

I think we don't.
« Last Edit: July 12, 2017, 02:25:04 PM by F.Tnioli »

steve s

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #13 on: July 12, 2017, 02:42:15 PM »
FT,

You do not seem to understand the material properties of ice and glaciers or the differences between ice shelves and glaciers. You set up straw men in situations that cannot exist and then talk of consequences that would be unlikely if they did exist. Study physics. Study ice. Learn about the ice topography of the Antarctic in more detail. And study the points that have been made in this thread for your benefit.

This website has some seriously competent glaciologists and few trolls. There is no ice conspiracy group here hiding a menace. 

Gray-Wolf

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #14 on: July 13, 2017, 03:07:46 PM »
Did a radar survey of ross not find some 'rucks' in the shelf as if it had halted at the front ( weight of contact on the sea floor below?) and piled up behind before the whole mass slowed to current flow rates?

If there is energy stored in this 'ruck' could the shelf not suddenly slip forward once the grounding line had retreated far enough to reduce the back pressure from sea floor contact? Would this then not act like a thrust fault and push the waters in front of the shelf in one beg shove the full depth of Ross Sea?

Just looking at ways of imposing such a large scale shunt on the water column and this was my best shot!
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DoomInTheUK

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #15 on: July 14, 2017, 01:26:22 PM »
FT - I'm just trying to ease any fears of a tsunami from ice sheet collapses. The almost instantaneous motion of the whole water column just isn't there at the scale you would need.

There might be some misconceptions here. A deep water wave is a circular motion within the water column with diminishing amplitude as depth increases. A tsunami looks like a wave, but is actually a displacement of the whole water column as the water flows away and tries to level out.

A tsunami acts as though it's a shallow wave in any depth of water.

http://www.soest.hawaii.edu/oceanography/courses_html/OCN201/littlepages/waves.html

So, is a tsunami possible - maybe, but not likely and it won't be very large. Is a big wave possible - almost certainly. However, a big wave will not travel thousands of miles at hundreds of miles an hour and wash away someones beach house.

To generate a tsunami we need a large volume displacement across the whole water column in a very short time frame. Undersea earthquakes with a vertical motion fit the bill. Large things falling into water (when a large fraction of them are already in the water)....less so.

GW - Yes. that's effectively an earthquake in the ice. I'm not sure if the dynamics allow it to happen, but it might be enough.

Of course, these calving fronts are fairly small in area when compared to the scale needed to produce big tsunamis. The boxing day one had a vertical displacement of 10's of feet over 600 miles long.

The energy then dissipates as the wave spreads out, so even if a tsunami was produced, from such a localised event it would count as a slightly bigger wave by the time it reached landfall.

FredBear

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #16 on: July 14, 2017, 02:09:44 PM »
FT - I'm just trying to ease any fears of a tsunami from ice sheet collapses. The almost instantaneous motion of the whole water column just isn't there at the scale you would need.



My thoughts:-
I agree +
A big meteorite in the wrong place would be the only possible trigger - and one in the rest of the oceans would be more likely because of their size. A massive earthquake might also start something but marine sediments are more likely to cause a tsunami than ice?(cf. Japanese earthquake, 2011)

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #17 on: July 14, 2017, 05:33:46 PM »
I believe an ice shelf is not uniform nor strong enough to amplify the wave it generates in a collapse. But, if you lose the buttressimg shelf fast enough the glacier (and the ground it resides) can become unstable and generate a land/ice slide tsunami. The main component here too would be land since it drops all the way to the bottom. So any tsunamis or waves involving ice are less damaging than tsunamis from plain landslides.
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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #18 on: July 28, 2017, 12:54:09 PM »
Should not be neglecting the prospect of abrupt isostatic rebound events. The huge volumes of fluid water and carbonate rich magma underlying the fringes of the continental shelves allow very big and abrupt uplifts, and trench block subductions when you lose large coastal ice mass. This is probably why lake Titicaca is full of oceanic species and remnant salinity with isotopic ratios identical to the Pacific. there is a tilted tide line down both the Andes and coastal range from Titicaca to the south that suggests the 12000ft high Altiplano was a gulf open to the Ocean to the south and all the indigenous people of south America tell of a massive uplift and Megatsunami sometime in the last 20000 years.
Very plausible for Greenland too. you go into a climate flip when suddenly its no stop heavy warm rain on Ice sheets, they will reach a level of soggyness that will allow cascade slumping all around the fringes.The Agassiz  burst event or events were probably slush slump rather than an actual subglacial or ice dammed actual lake. I'd be very concerned about Greenland as a priority once the Arctic loses its halocline and floods with warm Atlantic and Pacific waters to the surface. Torrential rain nonstop in winter on Greenland and you got maybe a week to get well inland and to decent altitude. And worldwide cascades of Storegga style underwater landslides would very possibly be triggered. Rapid ice loss probably triggered THAT one.
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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #19 on: July 28, 2017, 04:08:37 PM »
"abrupt isostatic rebound" just to add that when the ice melts here it'll move, much closer to the equator, ditto for greeenland.

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #20 on: July 28, 2017, 07:04:45 PM »
Should not be neglecting the prospect of abrupt isostatic rebound events. The huge volumes of fluid water and carbonate rich magma underlying the fringes of the continental shelves allow very big and abrupt uplifts,

How abrupt? How does the water and carbonates affect the asthenospheric viscoisty? Can you please support this with a reference? Typically viscous response to unloading gives maximum rates of <1cm/year. Hardly likely to have any impact in a number of human lifetimes.

FredBear

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Re: WAIS / EAIS eventual collapse question: huge tsunamies possible?
« Reply #21 on: July 28, 2017, 11:01:09 PM »
Hyperion, Storegga slides are thought to have been triggered by earthquakes & possibly amplified by destabilisation of methane hydrates in deposits formed under glacial conditions, not collapse of ice sheets. We may be surprised at the speed of change in polar regions but I feel there are more realistic problems than a tsunami from ice sheet collapse.