Okay, my Geography instructor just tried to instill the fear of Tsunami into me. Basically, he went into something that I've heard many times: That there's an island that's basically a dormant volcano (or something), that may break up. If it does, 1/4th of this island will go into the water, sending a Tsunami at North America that's 300 feet high. He then said, "It's not a matter of if, but a matter of when!" Then he said, "our lives are hanging by a thread".

My baloney detector is going off. How "possible" is this event? Is it truly a surety?

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Cumbre Vieja. 300m seems to be rather an overstatement for the wave height on arrival in the US (it's more like the early height on departure from the Canaries), but it's still going to be a bit of a problem for a large number of people around the Atlantic coasts.
Searching on "Cumbre Vieja" and "tsunami" will find you a lot more information.

Grant Hutchison

The island is La Palma is the Canaries. There seems to be a possibility of an extensive landslip which would displace enough of the sea to start a very substantial wave.

I've been told that there is no justification for a tsunami warning system in the North Atlantic. If in 2003 a prediction, in perhaps a television program, had been made of a possible disaster in the Indian Ocean due to an undersea quake, I wonder if it would have been dismissed as alarmist nonsense. Who knows?

Swiss researchers who have modelled the landslide say half a trillion tonnes of rock falling into the water all at once would create a wave 650 metres high that would spread out and travel across the Atlantic at high speed.

The wall of water would weaken as it crossed the ocean, but would still be 40-50 metres high by the time it hit land. The surge would create havoc in North America as much as 20 kilometres inland.

“If I was living in Miami or New York and I heard that the Cumbre Vieja was erupting, I would keep a very close eye on the news” - Prof Bill McGuire

"If the Cumbre Vieja were to collapse as one single block, it would lead to a giant mega-tsunami with an initial wave height of 650 metres. It would have a wavelength of 30 to 40 kilometres travelling westwards across the Atlantic at speeds up to 720 km/h towards America." - Prof Bill McGuire.

Incidentally, the three Storegga Slides count among the largest recorded landslides. They occurred under water on the edge of Norway's continental shelf (Storegga is Norwegian for "the Great Edge") in the Norwegian Sea, 100 km north west of the Møre coast, where an area the size of Iceland slid, causing a megatsunami in the North Atlantic Ocean.
This triggered 10-meter high tsunamis that hit north Scotland around 5,800 BC...

The largest wave in recorded history, was witnessed in Alaska in 1958, and was caused by the collapse of a cliff at Letuya Bay. The resulting wave was higher than any skyscraper on Earth and gouged out soil and trees to a height of 500 metres above sea level.

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There have been catastrophically large landslide caused tsunamis.

Luckily, they don't happen very often, like on a scale of 100,000 years.

The Islands of Hawaii have a long history of major slumps, the seafloor around the chain is littered with them.

One of the more geologically recent ones, on the Big Island near the Captain Cook monument, was large enough to cause waves that pushed coral blocks hundreds of feet up on Lanai.

In the more distant past, one of the biggest was the north side of Molokai, but also there were some really big slides on Oahu and on Kauai.

Edited to add, sometimes the Earth has a really really bad day (worse than the eruptions or tsunamis that have been observed in historical times). Sometimes a huge volcano like Santorini explodes, or a big asteroid hits, or a resurgent caldera like Yellowstone goes off, or a big slump causes a huge tsunami. One of these things could happen in the near future, or it could be 100,000 years from now. (shrug) That's the way it is, at least until we can do a better job of prediction, at least that would give us warning to do something if we could.

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Here's a nice map of Hawaii and the Sea Floor:

http://geopubs.wr.usgs.gov/i-map/i2809/

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there's a reasonably in-depth discussion about tsunami's in one of phil's movie reviews... not sure which. one of them thar doom and gloom cuts.

taks

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Here you can find further informations.

http://www.drgeorgepc.com/TsunamiMegaEvaluation.html

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Thanks, folks. BTW, Taks, I think you're thinking of "The Day after Tomorrow".

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Check out my writing, maybe.

mega tsunami is possible due to the wide planetary effect? sun, moon!
or it happens due to the jerk in rotations of the earth?as twice or thrice than the previous tsunami effects?

No, tsunamis are caused by earthquakes (where the sea floor shifts up or down) or by landslides (where material slides into the water).

This discussion has been about a very large tsunami that could be caused by a huge landslide, where a major part of an island slides into the sea.

Earthquakes and landslides do not seem to have any correlation to the sun or moon.

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I'll have to look it up somewhere.. but the landslide-tsunamis were popularized because of the ones that happened in those long, narrow bays in alaska and norway.

IIRC (and it's been awhile), you don't get the same effect from an island losing a chunk in the middle of the ocean as the shock wave spreads out into an ever-increasing arc.

I also strongly suspect that the total mass dropped is being calcuated simoultaneously. Landslides dont' often work that way. By that I mean that if the movement takes fifteen minutes to pass any given point, they're calculating it as it all passing in one second. And obvioulsy, once the start of the slide displaces the water, the stuff falling behind it has very little to do.

Of course that's just my thoughts on the modeling being done and what's been previously observed (read: it seems unlikely, don't it?)

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Could be the movie 'Deep-Impact' stars Robert Duvall, Morgan Freeman, Téa Leoni, Elijah Wood - movie about a comet on course for colliding with Earth,
later in the film a comet fragment hits the Earth ( Atlantic Ocean ) a wall of water rises up - the comet made tsunami about as fast as a jet aircraft and causes some major damage around the world

This was pretty much where the thinking of the possibility started.

Unless its a big enough chunk

See aurora's posts above. When I saw the title of this thread (before reading any posts) the first thing that popped into my head was nearly word for word what she wrote. This was imagined first after some detailed ocean floor mapping started several years ago. What was noticed were GYNORMOUS landslide patterns around the Hawaiian islands and all of the emperor seamount chain. What was finally concluded, was that the islands weren't eroding at a nice slow pace from the wave action, (the question had always been looking at the chain of islands that we should be able to watch the erosion if it were to account for the regular reduction in size of the islands as the plate moved) this answered that question. Huge chunks of the islands would catastrophically break off in a massive underwater land slide.

You've heard of the Big Crack, or the (don't remember the name) big canyon on Kauai? These are the start of this happening. Once it was recognized a search for the most likely next happening might be. The Canary islands are in the lead, however that could still be a few 100,000 years away… or we may see it in our lifetime…I’m betting we get some warning.

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yes, i know and understand that - however, looking at the spoilage does not mean that it all came down in one massive pile. Look at the spoil pile at the bottom of, say, Mount Rushmore. That happened over several years. Yet in a hundred thousand years you won't be able to tell whether it happened in one day or over a thousand years.

I'm not saying it can't happen. I'm saying that the pile isn't conclusive.

Furthermore, Lanai is smack dab in the middle of the chain. the wave hasn't had much time to dissipate. You're getting back into the "narrow area" again.

to reiterate: what we have here is a) visual observation of one phenomenon (tsunami-like waves in narrow inlets) b) notice of spoil piles off of islands similar to ones found after (a). c) the conclusion that if (a), (b), which at this point, is unwarranted.

however, to my knowledge, there really hasn't been any colclusive proof that mega-tsunamis are definitively caused by slidage. so until we get that, it seems just as likely that ocean-wide mega tsunamis can only be caused by massive earthquakes and hollywood.

btw, according to wikipedia the canary wave would be beween 30 - 70 feet. (i'm very inclined to go with the lower figure). Thats not going to get much more than a mile inland, if that. NYC would be wet, but essentially fine.

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And what if the slump comes off the far side of the island?

The footprint of eons of gradual rock falls and one catastrophic event are different, and well I guess I have to go with what i was told on this, but the fans at the base of the seamounts are interpreted as very large events.

Also we aren't talking about a bunch of rocks breaking away from a hillside and splashing into the water. We are talking about large portions of the island breaking away. Since it starts at sea level, it is reasonable to model this as all happening at once, as far as the mass of the rock displacing ocean volume. I understand you're issue with disapation, and whenever I see the guestimates about the size of a mega-tsunami i tend to go with the smaller figures as well, but the mechanism seems failry reasonable to me.

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The distance the slide traveled also says a lot about how much mass was involved. If you have stuff crumbling off over an extended period of time, you'll get nothing more than pile of rubble at the base, but if a very large chunk breaks off all at once, there's a lot of energy there...

Check out the link aurora posted previously. That debris field to the north of the islands certainly didn't crumble off over a significant period of time.

It was mentioned earlier: Lituya Bay, Alaska, 1958. Ocean-wide, ehh... It's definitely plausible, though.

isn't the official BAUT unit the furlong?
50 meters is about 164 feet, but I think the height of the water increases as it arrives at land, as the shallow coast concentrates its extent.

This paper features an interesting take on the issue. They talk about 25 m waves striking NA shores.

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Oops.
(I keep forgetting there are places in the world where "metres" isn't the natural unit of measurement. What is it now: the US, Liberia and Myanmar? )

Grant Hutchison

re: bas versus oceans and megatsunamis - please understand that you're talking about a change in several orders of magnitude and things don't always scale up. In other worlds, it's two different animals and not necessarily valid.

re: past slides off the Canaries. I've just read through the initial paper (which, btw... has been seriously criticized for its conclusions), and even the authors suggest that confirmation of this theorey depends on discovering confirmation evidence in the form of continent-wide deposition. At this point,according to the USGS (and you must recall the atlantic coastline is one of the most heavily studied coasts) there has been ZERO confirmation of this theorey. It really should be somehting as simple as looking up already existing core samples.

Lastly, apparantly subsuquent modeling of the event has exposed some of the problems with the initial model. Revised figures indicate wave heights of between 1 - 3 meters hitting the US shore.

http://library.lanl.gov/tsunami/ts193.pdf
(the atricle is on p. 37 of the pdf)

addendum: from the International Tsunami Information Center 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.

addendum to the addendum:
http://www.drgeorgepc.com/TsunamiMegaEvaluation.html
(a fairly long criticism to the original paper - don't mind the hawaiian colors, i think he's been doing research for too long in Hawa'ii )

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Yeah, and the unit of time is the fortnight. Right? ;-)

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I seem to remember that. Isn't the official unit of mass the slug?

I always liked the "cubit", whose exact length and origin are even more hazy than the "foot".

Of course it's more hazy--the foot is exactly 0.3048 meters.

or Bh0E'0 on Uranus

But Aren't both Krakatoa and Santorini relatively shallow explosions? Wouldn't a massive slide at LaPalma displace water to a significant depth increasing the amplitude?

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The paper I linked above (#20) features some math concernng the total mass of the flank slide.

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So there is already a well established scientific
institute there. Shouldn't be to much problem
to observe the mountain seismologically 24/7.

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