The horrible megatsunami, coming soon...

[shadron]

About ten years ago, the BBC, at loose ends, decided to locate and scare everyone with a whole new disaster-in-waiting, another Yellowstone caldera eruption (it's been so overdone) to raise awareness of the program's sponsors (at any rate the sponsors when it makes it to America), and keep the BBC relevant. I'll say at the outset that I really admire a lot of the BBC/Horizon doco output, but there are some times when even the best slip up. Casting about, they caught the eye of some scientists in London...

The result was Megatsunami!, a one hour doco on the scientific certainty of a monstrous wave in your future, if you happen to live on the eastern US seaboard. It seems a tsunami of monstrous proportions is headed your way, with the same inevitability as that of the next New Madrid earthquake.

The story starts out in a small (well, maybe 12 square mile) bay in southern Alaska called Lituya Bay. Geologists (in the 50s, so the story goes) noted that the coasts of the bay had been denuded of trees and topsoil up to a half kilometer above the bay, and while they had no ready answer, they took it under advisement for the time being. On July 9, 1958, a 7.7 earthquake caused a huge landslide at the top of the bay, and the resulting waves reached 1740 feet vertically up the slopes. There's a dramatic, but irrelevant story about a man and his son fishing on a boat in the bay that day, which the doco plays well up. So, now we know what caused the slope anomaly. Unfortunately, Wikipedia records that three other landslides have been witnessed in the bay: in 1854 (waves 395 feet high), 1899 (200 feet) and 1936 (490 feet), so I begin to feel there is as much weaving as telling of this story.

What if, the story continues, there is the possibility of scaling this local disaster up into something earth shaking? Enter the London scientists, Dr. Simon Day and Dr. Steven Ward of the Benfield Hazard Research Center of the University College of London. They have been investigating the scaling up of Lituya Bay into a world shaking theory of supertsunamis. In the doco, they concentrate on the Canary Island of Las Palmas off the African coast, which is principally the volcano Cumbre Vieja. A typical strato-volcano, its slopes are mainly loosely held ejecta, and are therefore prone to landslides, similar to avalanches between levels of loose material on a slope. One slope is on the western side of the island, with nothing between it and the US eastern seaboard but about 3400 miles of open Atlantic. If that slope were to slip into the Atlantic, why, we could expect a 100 foot wave on Miami Beach, for starters.

Proof: Well, they have some really neat computer graphics. One shows the difference between an ordinary tsunami (maybe 20, 30 ft tall at most, caused by a basement rock drop/rise) and a supertsunami (caused by a landslide), and it's, by george, 100 ft tall. Then there's a neat experiment at a Swiss (I think, can't be sure) facility where they slide a load of rocks into one end of a 5 foot wide tank maybe 50 ft long, and watch the water dramatically run up the slope at the other end. Finally, some friendly geologists wander about the island and note slippages on the slope, and gasp at dikes which must be holding the water high enough to lubricate the rocks (cue another experiment with a couple of bricks on a slope and a hose feeding water between them, and watch the top one slide off.) Some more graphics, including the typical tsunami graphic, with the red flame shape shooting out of the island towards - yes, the US coast, and some final words about 'not if, but when'.

I'm going to continue this thread with the research I've done and observations I've noted a little later. This little contretemps leads me to some odd conclusions about science, but I'd like to hear other opinions, must certainly from volcano, Correa Neto and/or Dinwar, and other scientists who may have stopped and looked at this, as well as opinions of anyone else interested. More to come.

Link to Megatsunami!:

YouTube Video This video is not hosted by the JREF. The JREF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.

I AGREE

This is just a trailer. The whole thing doesn't seem to be on YouTube any longer, though it used to be. No doubt it can be found somewhere on the net.

[Corsair 115]

I don't know if it's the same program, but I remember a show I saw a number of years ago on the Discovery Channel (Canadian version) that was on this same topic. From what I recall it seemed to be rationally plausible. If the side of that particular volcano does eventually collapse into the ocean, those millions of tons of rock are going to displace a hell of a lot of seawater.

[quarky]

We are so doomed.
I'd like to see a top ten list of our doomed-ness.
But I guess it would be off topic.
I live on the New Madrid fault, below a huge impoundment.

[ohms]

I remember the show in question and also that other scientists have since argued that the Cumbre Vieja volcano is quite unlikely to cause the kind of catastrophic landslides depicted in the programme. As far as the science goes, I don't think this was one of Horizon's better episodes.

[Soapy Sam]

Originally Posted by quarky

We are so doomed.
I'd like to see a top ten list of our doomed-ness.
But I guess it would be off topic.
I live on the New Madrid fault, below a huge impoundment.

...
of radioactive mine tailings wherein dwell mutated superbacteria...

[MG1962]

What makes you think the only evidence is from the Canary islands, or that such events have not occurred in recent times circa 1500AD on the Australian coast

[Marduk]

Originally Posted by quarky

We are so doomed.
I'd like to see a top ten list of our doomed-ness.
But I guess it would be off topic.
I live on the New Madrid fault, below a huge impoundment.

you need to be more worried by microbes than anything larger
http://across.co.nz/TenMajorCatastrophes.html

[NoahFence]

Not sure I understand the snarky tone - is this not a feasible possibility?

[Marduk]

Originally Posted by NoahFence

Not sure I understand the snarky tone

what snarky tone ?

Originally Posted by NoahFence

is this not a feasible possibility?

is what not a feasible possibility ?

[Correa Neto]

I remember similar claims regarding Hawaii, including the identification of the site of a possible past landslide.

Bear in mind that **** happens. The longer a species lingers around, the higher will be the odds a major **** will happen around its times. If human species lives long enough, it will be submitted to supervolcano eruptions, massive tsunamis, asteroid impacts, etc.

This put, I would, before entering the OMG! WE'RE SO SCREWED! mode, I would check for evidence. According to the documentaries I've seen, and IIRC them, there are indeed evidences of major tsunamis on eastern and western North America. OK... But are massive landslides on vocanic islands the only possible sources for these tsunamis? No. In the eastern shoreline, for example, lanslides at the continental shelve and the odd earthquake (close and far away) are also possible. In case of doubt, ask the Portuguese who lived in Lisbon in 1755 and Google for Grand Banks earthquake. The western shoreline, this one we already know its earthquake-induced tsunami risks.

So, what should you guys do if a tsunami register can actually be linked to a volcanic island collapse? Enter the OMG WE'RE SO SCREWED mode? No. First remember that for the megatsunami to happen, besides the computer models being right, some other circunstances are needed- an eruption must happen when the mountain is wet due to rains and the collapse must be sudden, happening at once. A whole moutainside creeping towards the sea for weeks, days or hours will be no case for worries. Episodic small collapses will cause small tsunamis, however.

Where do you go from here? I don't know! The ball is in the government's field, for good or for bad. Lets suppose your government thinks the risk is real. Real-time slope and sesimicity monitoring programs, evacuation plans and tsunami barriers would be created. The size of the barriers (as well as the areas to be evacuated) would depend on the calculated most likely maximum size of the waves and the economics of the required constructions. Here's a guess, straight out of the rear end of my disgestive system. The most likely wave is 5 meters high? OK. Barriers are buildable for a long stretch of the coast. 10 meters? Just around key assets. 30 meters? Pray the IPU it never comes or that it comes only after you manage to have a really good long-term forecast.

[jj]

The thing missing from the Canary Island scenario is that the distance attenuation component of the wave seemed to be missing.

[edd]

I think it's La Palma, not Las Palmas.

[Skeptic Ginger]

Originally Posted by jj

The thing missing from the Canary Island scenario is that the distance attenuation component of the wave seemed to be missing.

I think you might need to review the 12-26-04 Indian Ocean Tsunami.

These mega-disasters are unlikely in any one person's lifetime but 100% likely in some person's lifetime, if that makes sense. Not something to keep one from living in Florida or in the Cascadia Subduction Zone where I live, but not something I would dismiss altogether.

[Skeptic Ginger]

Originally Posted by Marduk

you need to be more worried by microbes than anything larger
http://across.co.nz/TenMajorCatastrophes.html

The bird flu HPAI H5N1 continues to smolder and genetically drift.

[shadron]

not yet...

[NoahFence]

Originally Posted by Marduk

what snarky tone ?


is what not a feasible possibility ?

The OP sure seemed snarky to me. Perhaps it was missing a few sarcasm icons?

[GlennB]

Originally Posted by jj

The thing missing from the Canary Island scenario is that the distance attenuation component of the wave seemed to be missing.

That was my first thought - the inverse square law (if that's right?).

The Japanese tsunami was born of a very long fracture - some 300 miles long IIRC - that was close to the coast. The Canary volcano is much smaller and distant from major population centres.

But don't quote me

[JeanFromBNA]

Originally Posted by NoahFence

The OP sure seemed snarky to me. Perhaps it was missing a few sarcasm icons?

I get the snark; the program is another version of "things the general public needs to worry about so that we (in the broadcast media) can keep our jobs."

There is already a lot to worry about. Manufacturing more worry via reminders of possible or probable natural disasters is just annoying.

[JeanFromBNA]

Originally Posted by quarky

We are so doomed.
I'd like to see a top ten list of our doomed-ness.
But I guess it would be off topic.
I live on the New Madrid fault, below a huge impoundment.

Quarky, my inlaws live in NE Arkansas, near the New Madrid. We have farmland near there that has sand blows from the last earthquake. Where do you live?

[Miss_Kitt]

Not to mention the effect on tsunami of trenches in the sea floor, which help dissipate some of the energy when the wave passes over them. I don't know the mapping of the ocean floor between the suggested landslide and the Atlantic Coast, but that would certainly have an effect.

In a somewhat related note, there are these "rogue waves" of extremely large size that appear to occur infrequently but not rarely in the open ocean. IIRC a recent survey of satellite data indicated that these waves, whose cause is still not understood well, were found to be much more frequent than had previously been suspected. Yet these waves are not striking shore--ergo, they are deteriorating en route.

A large enough seismic event, or a big landslide, certainly *can* trigger a tsunami; but the reason we have the Pacific tsunami warning system buoys in place is that so far we can't determine the factors that separate "can" from "will".

I rather enjoy the "We Could All Die Tomorrow" disaster scare-umentaries on Discovery and the Beeb. Sometimes they have useful information, and they can always lead to a good discussion with the kids. But I don't lose sleep over them, either.

I live in the Pacific Northwest, so my disaster-could-happen is a big earthquake. I am not in tsunami risk, but the chance for loss of power, natural gas leaks, disruption of communication and building collapses, road destruction, etc. of a major quake is ever present. Other than having a family plan for natural disaster and supplies to get through the critical first 3 to 5 days, there's not a lot that can or should be done.

Just my thoughts, MK

[shadron]

Originally Posted by NoahFence

Not sure I understand the snarky tone - is this not a feasible possibility?

My snarky tone is because I wanted to get some discussion going. I find my more usual dry fact tone doesn't normally do that. More about this later.

Originally Posted by Corsair 115

I don't know if it's the same program, but I remember a show I saw a number of years ago on the Discovery Channel (Canadian version) that was on this same topic. From what I recall it seemed to be rationally plausible. If the side of that particular volcano does eventually collapse into the ocean, those millions of tons of rock are going to displace a hell of a lot of seawater.

The typical earthquake tsunami displaces perhaps 30' of water over a thousand square miles, or cubic miles of water. Show me a cubic mile landslide. The 1958 landslide into Lituya Bay was 30 million cubic meters, or 0.0072 cubic mile.

Originally Posted by Skeptic Ginger

I think you might need to review the 12-26-04 Indian Ocean Tsunami.

These mega-disasters are unlikely in any one person's lifetime but 100% likely in some person's lifetime, if that makes sense. Not something to keep one from living in Florida or in the Cascadia Subduction Zone where I live, but not something I would dismiss altogether.

The thesis in the program is that earthquake-caused tsunamis are limited in height to the vertical displacement of the ocean floor, typically being 30-40' for major earthquakes. The ones caused by landslides are not so limited, and thus are "supertsunamis" (their words. not mine). This falls well within my definition of a falacious argument (more anon), but that's what they are saying. I'm well aware, and respectful, of earthquake tsunamis. And yes, Cascadia is one of those places; I live near Denver, well within the range of a Yellowstone caldera event, and even closer to the largest volcanic caldera event known in history, called the La Garita. Good luck to all of us, and I mean that.

Originally Posted by jj

The thing missing from the Canary Island scenario is that the distance attenuation component of the wave seemed to be missing.

Yes. That was the first thing that grabbed me too, when I saw that ridiculous box of rocks experiment. The wavefront doesn't race in a tunnel across the Atlantic, it disburses across at least 180 degrees, and more; it is a distance squared problem, not linear. Of course, that is the same as earthquake tsunamis, indeed earthquake tsunamis generally disburse over 360 degrees, as they usually occur is deep ocean, so this problem with the supertsunami analysis is true and valid, but it's not the whole story.

And many scientists seem to agree: http://www.lapalma-tsunami.com/mader_lapalma.pdf

Originally Posted by MG1962

What makes you think the only evidence is from the Canary islands, or that such events have not occurred in recent times circa 1500AD on the Australian coast

True. The historical event of a landslide at Mt Etna in 8000 BCE was the best example of a supertsunami I could find, and yet all the evidence about its size (50-100 meters high around the Med) and devastation is somewhat shakey and equivocal. The tsunami you mention is the work of one scientist, Dr. Bryant of Woolongong University, and I can find no where where he mentions what he thinks the cause of the tsunami is. As I said above, I have respect for earthquake caused tsunamis, but I question the notion that landslides can be so hugely different as to merit a new term, supertsunami.

Originally Posted by quarky

I'd like to see a top ten list of our doomed-ness.
But I guess it would be off topic.
I live on the New Madrid fault, below a huge impoundment.

Jezus, Quarky, head for the hills. Say, 500 miles an any direction but south.

Originally Posted by Marduk

you need to be more worried by microbes than anything larger

I agree with that, personally.

[NoahFence]

Originally Posted by JeanFromBNA

I get the snark; the program is another version of "things the general public needs to worry about so that we (in the broadcast media) can keep our jobs."

There is already a lot to worry about. Manufacturing more worry via reminders of possible or probable natural disasters is just annoying.

I found the episode very enlightening, and informative. Seems to me that I'm right smack-dab in the path of this thing, but I'm not worried about it.

[shadron]

Originally Posted by Miss_Kitt

Not to mention the effect on tsunami of trenches in the sea floor, which help dissipate some of the energy when the wave passes over them. I don't know the mapping of the ocean floor between the suggested landslide and the Atlantic Coast, but that would certainly have an effect.

I hadn't given that much thought, though its a part of another argument that I have concerning power coupling. You may note that the one big obstacle in the way is the Mid-Atlantic Ridge, and it is no small obstacle.

Quote:

In a somewhat related note, there are these "rogue waves" of extremely large size that appear to occur infrequently but not rarely in the open ocean. IIRC a recent survey of satellite data indicated that these waves, whose cause is still not understood well, were found to be much more frequent than had previously been suspected. Yet these waves are not striking shore--ergo, they are deteriorating en route.

I think the current thinking on them is resonance effects involving multiple coupled bodies of water, and interference /reinforcement patterns.

Quote:

A large enough seismic event, or a big landslide, certainly *can* trigger a tsunami; but the reason we have the Pacific tsunami warning system buoys in place is that so far we can't determine the factors that separate "can" from "will".

Yes, and hooray for initiating such a project in the Indian Ocean. It's never too late to prepare.

Quote:

I rather enjoy the "We Could All Die Tomorrow" disaster scare-umentaries on Discovery and the Beeb. Sometimes they have useful information, and they can always lead to a good discussion with the kids. But I don't lose sleep over them, either.

I spend a fair amount of time trying to defuse and explain the science for these sorts of videos. Interesting work in retirement.

Quote:

I live in the Pacific Northwest, so my disaster-could-happen is a big earthquake. I am not in tsunami risk, but the chance for loss of power, natural gas leaks, disruption of communication and building collapses, road destruction, etc. of a major quake is ever present. Other than having a family plan for natural disaster and supplies to get through the critical first 3 to 5 days, there's not a lot that can or should be done.

Just my thoughts, MK

I don't know how to tell you this, MK, but the fact that you live in a subduction zone is plenty of reason to be aware for tsunamis. After all, the Pacific Ocean is known for its tsunamis, and the reason why it should be so is because it is surrounded on all sides by subduction zones. Japan's tsunami was caused by one, as was the Boxer Day disaster (not Pacific, but still subduction); a major quake off the Oregon coast in 1700, a magnitude 8.7 to 9.2 megathrust earthquake, caused a tsunami that was recorded in Japan, and records far above waterline in Oregon do as well. Earthquakes anywhere else in the world cause few tsunamis, and those that do are mostly to to subduction. On the Pacific Coastline, anywhere, an earthquake should be followed immediately with thoughts of a potential tsunami. While the Olympic Peninsula is no Aceh peninsula, Seattle could still see considerable flooding.

[truethat]

Years and years ago I was told by a college professor that if the planet's climate heats up it could cause the Antarctic circle to flip over due to a disparity in weight or some other such nonsense, and then we'd get a tsunami that would wipe out South America and half of Texas.

[Skeptic Ginger]

Originally Posted by shadron

not yet...

Are you talking about HPAI H5N1?

Scientists Brace for Media Storm Around Controversial Flu Studies

Ferreting Out Influenza H5N1

Quote:

A laboratory in the Netherlands has identified a lethal influenza H5N1 virus strain that is transmitted among ferrets. These findings are under review by the National Science Advisory Board for Biosecurity (NSABB) to ensure that they do not constitute a threat to human health.

Influenza in ferrets is considered to act the same among humans. The hope is there will be no natural selection pressures in the wild that mimic the forced mutation in the lab but the study shows the genetic changes are possible.

And the evidence in the wild is mutation and genetic drift are ongoing:

Highly Pathogenic Avian Influenza (HPAI) H5N1 Virus in Asia: Evolution and Vaccination

Quote:

HPAI (H5N1) is still an important emerging disease posing threat on both human and animal health. The causative agent continues to evolve rapidly within various poultry populations and may cause unpredictable outcome

Establishment of multiple sublineages of H5N1 influenza virus in Asia: Implications for pandemic control

Genetic analysis of influenza A virus (H5N1) derived from domestic cat and dog in Thailand

Evolutionary Dynamics and Emergence of Panzootic H5N1 Influenza Viruses

[truethat]

This is a tsunami thread Skeptic Ginger, can you at least keep your H1N1 fear mongering in the appropriate threads? We've been listening for about a year now to your scientific certainty of a world wide epidemic that never seems to show up. LOL

[Skeptic Ginger]

Originally Posted by GlennB

That was my first thought - the inverse square law (if that's right?).

The Japanese tsunami was born of a very long fracture - some 300 miles long IIRC - that was close to the coast. The Canary volcano is much smaller and distant from major population centres.

But don't quote me

When in doubt, find some scientific data:

Cumbre Vieja Volcano -- Potential collapse and tsunami at La Palma, Canary Islands

Quote:

Evolution of the La Palma landslide tsunami from 2 minutes (a, upper left) to 9 hours (i, lower right). Red and blue contours cover elevated and depressed regions of the ocean respectively and the yellow dots and numbers sample the wave height, positive or negative, in meters. Note the strong influence of dispersion in spreading out an original impulse into a long series of waves of decreasing wavelength. See also that the peak amplitudes generally do not coincide with the first wave. Even after crossing the Atlantic, a lateral collapse of Cumbre Vieja volcano could impose a great sequence of waves of 10-25 m height on the shores of the Americas.

And then see if the research is credible or controversial within the field.

Tsunamis within the Atlantic Ocean

Quote:

arious modeling simulations of the Cumbre Vieja tsunami event are available for viewing via the University of California Santa Cruz (download required Apple QuickTime)

Although the flank instability of Cumbre Vieja is noted, many scientists tend to disagree with massive failure of the western flank of the volcano; rather, they think it would happen in smaller separate events that would not be capable of triggering a mega-tsunami (Wynn and Masson, 2003). There is much scientific debate over the timing of an eruption that would trigger such events (considered to be decades to thousands of years), whether or not a massive failure of Cumbre Vieja's flank would occur during an eruption, or even if a mega-tsunami could possibly result (and reach the United States with such projected wave sizes). Mader (2001) used different wave modeling and determined that the resulting tsunami waves that reached the U.S. east coast and Caribbean would be on the order of 3 meters. The International Tsunami Information Center provided the following information in regards to the creation of a mega-tsunami by massive flank failure:

While the active volcano of Cumbre Vieja on Las Palma is expected to erupt again, it will not send a large part of the island into the ocean, though small landslides may occur.
No such event - a mega tsunami - has occurred in either the Atlantic or Pacific oceans in recorded history.
The colossal collapses of Krakatau or Santorin (the two most similar known happenings) generated catastrophic waves in the immediate area but hazardous waves did not propagate to distant shores. Carefully performed numerical and experimental model experiments on such events and of the postulated Las Palma event verify that the relatively short waves from these small, though intense, occurrences do not travel as do tsunami waves from a major earthquake.
To view more information on the scientific debate of Cumbre Vieja and a mega-tsunami, see the following links:

International Tsunami Information Center
Dr. George Pararas-Carayannis - Evaluation of Mega-Tsunami
Mader (2001)
Benfield Hazard Research Center

Links are embedded in the article.

[Skeptic Ginger]

Originally Posted by truethat

This is a tsunami thread Skeptic Ginger, can you at least keep your H1N1 fear mongering in the appropriate threads? We've been listening for about a year now to your scientific certainty of a world wide epidemic that never seems to show up. LOL

I was replying to Marduk and Shadron. Perhaps you should complain to the initiators of the side track instead of to someone further down the chat chain.


And you haven't been reading my fear mongering, I'm not afraid. You have been reading scientific papers and opinions that are relevant to the threat.

Oh, and BTW, a smoldering fire can either die out or erupt in a conflagration. I'm not predicting which way the H5N1 will go. I'm merely pointing out the threat is not over.

[CapelDodger]

Originally Posted by Miss_Kitt

Not to mention the effect on tsunami of trenches in the sea floor, which help dissipate some of the energy when the wave passes over them. I don't know the mapping of the ocean floor between the suggested landslide and the Atlantic Coast, but that would certainly have an effect.

I'm not so sure about that if the wave-travel is along the trench. I think then the trench will tend to channel the energy. I've read that there's a trench of Portugal's coast which has this effect on normal Atlantic waves, which rear up into monsters a few kilometres off-shore. A surfer might know more about that.

Quote:

I rather enjoy the "We Could All Die Tomorrow" disaster scare-umentaries on Discovery and the Beeb. Sometimes they have useful information, and they can always lead to a good discussion with the kids. But I don't lose sleep over them, either.

I'm of the same opinion. TV Science can't all be dry, and as you say, Horizon programs do normally contain information. (The standard has fallen off recently; most things BBC have recently, but not Sir David Attenborough, may his tribe increase.) The program in question smuggled some geology through to the unwary, for instance .

The La Palma tsunami would probably be bad news for us in Cardiff as it would be amplified by the Bristol Channel. At low tide we'd probably be OK though, and the yuppie-flats around the Bay would break a lot of the force if there's any justice (which there ain't, of course).

[shadron]

Originally Posted by Skeptic Ginger

Originally Posted by shadron

Not yet...

Are you talking about HPAI H5N1?

Scientists Brace for Media Storm Around Controversial Flu Studies

Ferreting Out Influenza H5N1Influenza in ferrets is considered to act the
...

Actually, I was not. I was composing my magnum opus below that, and accidentally hit Submit; such is my physical state that sometimes my fingers race beyond my brain.

I have no problems with your contentions on HxNx; I'm not enough a public health expert to really comment on that.

[Marduk]

Originally Posted by truethat

Years and years ago I was told by a college professor that if the planet's climate heats up it could cause the Antarctic circle to flip over due to a disparity in weight or some other such nonsense, and then we'd get a tsunami that would wipe out South America and half of Texas.

his name wasn't "Charles Hapgood" was it ?


far more people have died in floods than Tsunamis, Tsunamis kill thousands, floods kill millions and aren't limited to coastal areas

[truethat]

Originally Posted by Skeptic Ginger

I was replying to Marduk and Shadron. Perhaps you should complain to the initiators of the side track instead of to someone further down the chat chain.


And you haven't been reading my fear mongering, I'm not afraid. You have been reading scientific papers and opinions that are relevant to the threat.

Oh, and BTW, a smoldering fire can either die out or erupt in a conflagration. I'm not predicting which way the H5N1 will go. I'm merely pointing out the threat is not over.

I know I know, we've been hearing your fear mongering again and again inserted into every thread possible. It's kind of amusing actually.

Hey there's a new movie coming out you might like.

http://www.imdb.com/video/imdb/vi3924270105/

You actually sound a bit like those "End of Times" people who keep predicting the end of the world, then when it doesn't happen on the day they said it would they won't admit they were wrong, it's just back to the drawing board for more. Don't worry I'm just teasing you, you actually are kind of amusing.

Originally Posted by Marduk

his name wasn't "Charles Hapgood" was it ?


far more people have died in floods than Tsunamis, Tsunamis kill thousands, floods kill millions and aren't limited to coastal areas

People like drama, it's about terror and fear in more ways than one. A MegaTsunami has so much more panache and fear in it than just a simple flood, even though floods do cause more death and damage.

[shadron]

Originally Posted by CapelDodger

I'm not so sure about that if the wave-travel is along the trench. I think then the trench will tend to channel the energy. I've read that there's a trench of Portugal's coast which has this effect on normal Atlantic waves, which rear up into monsters a few kilometres off-shore. A surfer might know more about that.

Actually I think she was saying that whatever unevenness got in the way as it crossed the Atlantic would tend to cause it to dispurse more. That brings up another aspect of the Way Things Work for tsunamis.

The energy imparted on the water by an earthquake is truly tremendous; Tsunamis caused by nuclear weapons have proved to be disappointing to most observers. The famed Crossroads/Baker underwater test had only three foot waves beating ion the Bikini atoll shore six mile away from the blast. Cubic miles of water rise or fall (usually fall, gravity being what it is) because the floor of the ocean, for thousands of square miles, can suddenly do just that. Subsidence areas are particularly prone to that; the theory is that the subsiding plate drags the edge of the continental plate down with it as it slides downward, building tension in the continental plate. When that gets relieved, the normal motion is for the continental plate to lengthen and drop, straightening itself. That drops not just the plate, but the whole column of water above it. This normally happens at sea and to a lesser extent on the edge of the plate, on dry land. Commonly far enough out to sea as to cause the column to be in deep water, up to two miles deep.

The depth doesn't make the energy higher, but what it does do is cause the disturbance to couple very well with the ocean water. In engineering we often talk about impedance matching; the idea that maximum power is transferred when the source and the sink suffer little or no discontinuity between them. That is why, for example, speakers and amplifier outputs are matched for impedance, because the maximum power is transferred, and with minimal distortion. When the source of energy is this big - thousands of square miles, then maximal energy is transferred when as much water as possible is engaged. A landslide, it seems to me, doesn't have the same engagement; it takes place (by definition) at the thin edge of a landmass, it pushes the water slower than the earthquake does.

That energy begins to travel outward. In the earthquake model, it has a relatively uniform vertical profile to negotiate; the ocean will stay deep until it nears land at the end of the journey. In the landscape model, the first thing to be negotiated is the shallows passing into the deeps. In the beginning it is a tall surface wave, as there is limited water. So it first has to transform itself into a typical deep ocean tsunami wave (which is actually a change in kind: surface waves and tsunami waves move differently), and that expends energy, and in my experience, probably doesn't ever totally take place; the truly deep water involvement of the earthquake wave isn't shared by the landslide one. Only after that are the waves comparable (something not taken at all into account in the graphic on how a supertsunami waves is so much higher than the earthquake wave, out at sea.

This has been a very qualitative discussion of tsunamis and their creation and life. With regard to the ocean floor, since the deep water is more involved in an earthquake wave than the other, it is likely that the floor roughness will more dissipate it a little faster. In the Pacific, there is, for the most part, little to get in the way - just the occasional island and atoll. It would be interesting to determine what the effect of the Atlantic Ridge would be on real tsunamis.

[CapelDodger]

Originally Posted by shadron

Actually I think she was saying that whatever unevenness got in the way as it crossed the Atlantic would tend to cause it to dispurse more.

That's why I specified trenches along the line of wave-travel. We can't say generally that trenches will sap wave-energy. Wide (relative to the wave-front) discontinuities, such as the Mid-Atlantic Ridge, will tend to sap energy.

Quote:

That brings up another aspect of the Way Things Work for tsunamis.

The energy imparted on the water by an earthquake is truly tremendous; Tsunamis caused by nuclear weapons have proved to be disappointing to most observers.

When a subduction zone jerks it beats everything for energy. The next step up is solar flares. Volcanoes, even at their most explosive, are loud and telegenic and nasty to live by but it's all show in comparison. The same applies to nuclear weapons.

It's good to have a sense of scale.

[IIIClovisIII]

Thought you were talking about La Cumbre Vieja.

That thing has like 500 billion cubic meters of rock ready to fall into the ocean?

[Checkmite]

Originally Posted by shadron

True. The historical event of a landslide at Mt Etna in 8000 BCE was the best example of a supertsunami I could find, and yet all the evidence about its size (50-100 meters high around the Med) and devastation is somewhat shakey and equivocal. The tsunami you mention is the work of one scientist, Dr. Bryant of Woolongong University, and I can find no where where he mentions what he thinks the cause of the tsunami is. As I said above, I have respect for earthquake caused tsunamis, but I question the notion that landslides can be so hugely different as to merit a new term, supertsunami.

I would be more inclined to consider the case of Krakatau in 1883, in the Sunda Strait (west of Java). At the end of the eruption, the rather sizable island subsided very quickly and almost completely, creating a massive tsunami responsible for nearly all of the event's casualties. But where the wave was immense and devastating inside the strait* surrounding the volcano, where the wave propagated outside the strait (and it propagated over a significant area of the Earth's surface) it was not destructive in any sense and in many cases would likely not have even been noticed had scientists not been specifically looking for it. Not even very nearby Australia reported any damage, IIRC.

* By "immense and devastating", I mean "the Apocalypse had stopped by briefly for a visit".

[MG1962]

Originally Posted by Checkmite

I would be more inclined to consider the case of Krakatau in 1883, in the Sunda Strait (west of Java). At the end of the eruption, the rather sizable island subsided very quickly and almost completely,.

I am not entirely sure your description of the eruption is all that accurate

[Skeptic Ginger]

Originally Posted by truethat

I know I know, we've been hearing your fear mongering again and again inserted into every thread possible. It's kind of amusing actually.

Hey there's a new movie coming out you might like.

http://www.imdb.com/video/imdb/vi3924270105/

You actually sound a bit like those "End of Times" people who keep predicting the end of the world, then when it doesn't happen on the day they said it would they won't admit they were wrong, it's just back to the drawing board for more. Don't worry I'm just teasing you, you actually are kind of amusing.

I've seen the movie, it's not new and "coming out", it's been out more than 3 months, and for the record, your view on the bird flu is over-simplistic and naive.

But back to the topic.

[shadron]

Originally Posted by IIIClovisIII

Thought you were talking about La Cumbre Vieja.

That thing has like 500 billion cubic meters of rock ready to fall into the ocean?

That's about 112 cubic miles of rock.

Do you know how Day and Ward computed that total? I don't, but I wish I did. My napkin computations seem to say they took the entire volume of the bottom third of the island (all that is south of the caldera), both east and west, assuming a constant slope from shore to peak of the ridge, and counted right down to sea level. That seems like a pretty good landslide. Even smooth avalanches don't go that far.

[shadron]

Originally Posted by Checkmite

I would be more inclined to consider the case of Krakatau in 1883, in the Sunda Strait (west of Java). At the end of the eruption, the rather sizable island subsided very quickly and almost completely, creating a massive tsunami responsible for nearly all of the event's casualties. But where the wave was immense and devastating inside the strait* surrounding the volcano, where the wave propagated outside the strait (and it propagated over a significant area of the Earth's surface) it was not destructive in any sense and in many cases would likely not have even been noticed had scientists not been specifically looking for it. Not even very nearby Australia reported any damage, IIRC.

* By "immense and devastating", I mean "the Apocalypse had stopped by briefly for a visit".

Yes, I agree with that assessment. No one knew what had happened until the Dutch got the ship in the harbor out.