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Mega-Tsunamis from Landslides

  1. Aug 27, 2005 #1
    Have you guyz heard about these Mega-Tsunamis? They form from large landslides and can be much taller and more desructive than a tsunami. A show on discovery said that a part of La Palma island off Africa is gonna break off in like a century or so. It would create a huge wave headed to America. Whats your opinions on this?

    They showed this on a show on discovery, and they may have exaggerated some things because Wikipedia said different stuff.

    http://en.wikipedia.org/wiki/Megatsunami

    and the discovery show was
    http://dsc.discovery.com/schedule/e...d=0&channel=DSC
    but the link says little about it.
     
  2. jcsd
  3. Aug 27, 2005 #2
    Well, hypes are quite popular nowadays since we don't seem to face the nuclear winter anymore.

    For a counter expertise opinion:

    http://www.lapalma-tsunami.com/

    Having been there myself (awesome island), I have not seen any evidence of those dropping blocks indeed.
     
  4. Aug 27, 2005 #3
    Thanks for the website. I had a feeling they were exaggerated this, and many of the facts made no sense or didn't add up. I figured the media would twist and make up many things.
     
  5. Aug 27, 2005 #4

    LURCH

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    I tend do imediately discount any source that starts with a statement like:

     
  6. Aug 27, 2005 #5

    Ivan Seeking

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    I agree. It's better to stick with reputable sources.

    http://www.sciam.com/article.cfm?articleID=0006DF17-5A60-1C61-B882809EC588ED9F

    http://t14web.lanl.gov/Research/TDAC2000/mader.tsunami.00.pdf
     
    Last edited: Aug 27, 2005
  7. Aug 28, 2005 #6

    Integral

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    I also have seen the Discovery channel show on Mega Tsu. I was not real impressed with the experimental setup they used nor was I convenced that it would accuratly reflect what would happen in a deep water large ocean invironment. The apparatus they used may well model the Alaska mega Tsu very well but it is not clear that they considered that in a ocean environment the wave would spread on a circiular front, the wave that strikes the US coast line would be part of a wave with a radius of several thousand miles, this would spread the energy of the souce over a tremoundous area of the ocean.

    Qualifier, I have not done any of the computations, perhaps the researchers did a better job then was presented on the TV.
     
  8. Aug 28, 2005 #7

    Ivan Seeking

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    Hundreds of terrorists wielding crowbars and large levers have been spotted on La Palma island.
     
  9. Aug 28, 2005 #8
  10. Aug 29, 2005 #9

    matthyaouw

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    It does strike me as a bit of a poor example really. The dimensions are hardly representative of a large ocean.

    My computer seems to refuse to view PDFs, so forgive me if the point has been addressed in any of the articles linked to here.
     
  11. Aug 29, 2005 #10

    LURCH

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    Yeah, I agree that the model and the one observed example leave a huge gap to leap when we try to model ;arger waves in the deep ocean. However, haven't geologists found evidence of wave impacts at hundreds of meters in altitude on both the Hawian and Coastal mountain ranges?
     
  12. Aug 30, 2005 #11

    matthyaouw

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    I can't remember where I heard this, but some believe that other factors like local uplift and subsidence can account for the sediment found on the Hawaiian Islands.
     
  13. Sep 9, 2005 #12
    MEGA TSUNAMI DISASTER that faces the US

    I also saw the program on discovery and posted about it under my first member ID Amp (since then I haven't been able to use it-forgot password). But getting back to the topic, the mega tsunami would be caused by a large hunk of the island plunging in to the ocean. This break off of a chunk of the island is caused in part by the active volcanism in the island, there are vertical shafts through out a fairly large area of the island - centrally located which are filled with or partially filled with water (from the last eruptive cycle of the islands volcano), what has been posited to happen is in the event of a new upwelling of magma, this water would be super heated, turning into steam under tremendous pressure because the previously mentioned vertical shafts are capped. The pressure of this steam it is thought will be great enough to cause huge areas of the island to slough off falling into the ocean on either side of the island this is what would generate the tsunamis. These tsunamis would indeed spread like a ripple similar to throwing a stone in a pond but once they reached the continental shelf traveling to the east coast of the US, they would behave like the waves that come ashore at Hawaiis' famous shores, towering as they build up to a crest. :surprised :eek: :eek:
     
    Last edited: Sep 9, 2005
  14. Sep 9, 2005 #13

    LURCH

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    Just saw this article, which talks about evidence of marine fossils at over 1,000 ft altitude in an area where the rate of uplift is considered to be pretty well undeerstood, on the island of Kohala.
     
  15. Sep 10, 2005 #14

    matthyaouw

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    Interesting, thanks. A megatsunami does seem to be the most probable cause.
     
  16. Oct 10, 2005 #15
    It's technically not a megtsunami, but it's still pretty big.
    Around 8100 years ago, one of the largest landslides in the world occurred at Storegga, 100 kilometres north west of the Møre coast. An area the size of Iceland slid into the Norwegian Sea.
    The slide, which ended up at a depth of 300-2500 metres, created a 10-20 metre high tidal wave that reached the Norwegian coast.
    The mass slid around 800 kilometres into the deep sea, and its back edge is around 300 kilometres long. The Ormen Lange field is in the middle of the depression left behind by the Storegga slide and is close to the steep slide edge which rises 200-300 metres up towards the continental shelf.

    From http://www.ormenlange.com/en/about_ormen/key_features/storegga_slide/
     
  17. Oct 10, 2005 #16
    However, it was the largest recent continental slope landslide on record with 3500+ cubic kilometers and may have caused the indications that we interpret as the Holocene 8100bp cold event. Furthermore the preceeding clathrate decomposition killed the mammoths:

    https://www.physicsforums.com/showthread.php?t=80137
     
  18. Oct 10, 2005 #17
    I think I saw the documentary in question and it left me with a couple of questions.
    Surely what would be as important as the volume of rock is the speed at which it moved? The model they were using to demonstrate this event looked to me as if it could just slide gracefully into the sea. It could only reach a decent speed by accelerating couldn't it? Wouldn't this cause it to break up?

    The other point is that what is so damaging with a tsunami is not so much the height of the wave but its length from front to back. More accurately I suppose its the volume of water it contains. Could a relatively small mountain/hill really move anywhere near as much water as the raising of the seabed did in last year's tsunami?
     
  19. Oct 11, 2005 #18
    I wouldn't call 3500 cubic kilometres small. Let's do a back of the envelope calculation for the tsunami.
    Greatest movement was 30ft or 30mtr? I don't remember. We'll take worst case. That's the movement at the epicentre. As we move back it diminishes. But we'll take worst case and assume it doesn't. Epicentre to coastline. Say 100kms. (I'm sure it's less, but worst case again.) Over what length? Let's say 1000kms. So the volume of rock moved = 1000 x 100 x 0.03 = 3000.
    So, at a maximum, with unrealistic worst case scenarios for each number the tsunami just manages to come in at the same order of magnitude as the Norwegian slide.
     
  20. Oct 11, 2005 #19
    I think I didn't make my post clear. I was refering to the island of La Palma that the original quetion was about. I think I'm right in saying that the whole island is only about 15 km x 8km, I can't remeber how high it is but I'm sure it could be high enough to give a volume of 3000 cu Km!

    I also seem to remember an article in the press saying that the sea around the island wasn't deep enough to allow the mountain to slide into it, which would also limit the effect!
     
  21. Oct 11, 2005 #20
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