Mega-Tsunamis from Landslides

JustStuit

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.

Andre

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.

JustStuit

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.

LURCH

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

Ivan Seeking

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

http://www.sciam.com/article.cfm?art...82809EC588ED9F

http://t14web.lanl.gov/Research/TDAC...tsunami.00.pdf

Integral

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.

Ivan Seeking

Hundreds of terrorists wielding crowbars and large levers have been spotted on La Palma island.

Andre

http://www.lapalma-tsunami.com/mader_lapalma.pdf
http://homepage.eircom.net/~rockyent..._Palma_grl.pdf

It still occurs to me that the numbers may be slightly exagarated.

matthyaouw

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.

LURCH

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?

matthyaouw

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.

Amp1

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.

LURCH

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.

matthyaouw

Interesting, thanks. A megatsunami does seem to be the most probable cause.

Ophiolite

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_o...toregga_slide/

Andre

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:

http://www.physicsforums.com/showthread.php?t=80137

Cybersteve

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?