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"Franz Heymann" wrote in message ... "Sacha" wrote in message k... On 3/1/05 11:30, in article , "Cerumen" wrote: wrote in message ... On Sun, 2 Jan 2005 16:09:33 -0000, "Bob Hobden" wrote: The main risk is the big piece of rock which is expected to fall off an island in the Canaries, generate a tidal wave that will wipe out the East Coats of the USA and not do a lot of good to the low countries. Apparently a tsunami hit the west coast of Ireland in 1775 ? after a seismic event near the Azores and Canaries causing some considerable damage.. A recent article I read somewhere said that if the predicted bit of La Palma falls off in one slab the resulting tsunami will lead to the disappearance of the Isles of Scilly (among other damage!) As well as New York Franz Lots of people have said that, but it seems unlikely. To create a tsunami requires a high energy shock wave, a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance, although there would certainly be a large wave locally much as when large icebergs break off. -- Charlie, gardening in Cornwall. http://www.roselandhouse.co.uk Holders of National Plant Collection of Clematis viticella (cvs) |
#2
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Charlie wrote:
To create a tsunami requires a high energy shock wave, a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance This is contentious. Have you read http://www.benfieldhrc.org/CentreNew...es/tsunami.htm or http://www.bbc.co.uk/science/horizon...anscript.shtml More recent suggestions that it would break up before falling, and "only" cause a wave 2 to 3m high have been made: http://news.bbc.co.uk/1/hi/sci/tech/3963563.stm . That page has links to sites that support and oppose the original tale. It boils down to "we can't know the future". |
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On Tue, 04 Jan 2005 10:01:05 +0000, Sacha wrote:
On 4/1/05 9:11, in article , "Charlie Pridham" wrote: snip Lots of people have said that, but it seems unlikely. To create a tsunami requires a high energy shock wave, a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance, although there would certainly be a large wave locally much as when large icebergs break off. But isn't the chunk of La Palma predicted to fall into the sea following volcanic action? Yes, but the eruption may not need to be vary large, just the right sort that lets water in behind the slipping section. -- Tim C. |
#6
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On Tue, 4 Jan 2005 09:11:41 -0000, Charlie Pridham wrote:
Lots of people have said that, but it seems unlikely. To create a tsunami requires a high energy shock wave, a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance, although there would certainly be a large wave locally much as when large icebergs break off. Rubbish. The speed of rock falling determines the wavelength of the wave, this would determine wether it travels more or less straight or would be diffracted around land masses. We are talking somewhat bigger bits of rock than icebergs dropping off a glacier in to the sea. Issue 2259 of New Scientist magazine, 07 October 2000: "It's hard to imagine what would happen if half a trillion tonnes of rock slid into the sea. But Hermann Fritz, a PhD student at the Swiss Federal Institute of Technology in Zurich, has spent several years modelling how landslides generate waves when they fall into water. Earlier this year, he constructed a lab model of the western flank of the Cumbre Vieja in a wave tank. The model is an elongated wedge-shaped block resting on a 10-degree slope with the tip of the block lying just under the water. When the block is released, it slides down the slope generating a wave, which is recorded by a high-speed camera. Fritz found that the sliding block generated a long, shallow, fast-moving wave¡Xthe classic profile of a tsunami. Scaling up 10,000 times, the model predicts that in real life the crest of the wave generated by the collapse of the western flank of the Cumbre Vieja would initially be a staggering 650 metres above normal sea level, more than enough to submerge the tallest building in the world. Fritz admits that there is a big size difference between his model and the real tsunami, but he has no doubt that the dimensions of the wave are in the right ballpark." and NS 29 August 2001: "When the La Palma volcano caves in, Ward says it will trigger a series of around ten waves, spaced about a hundred kilometres apart. As they reach the shallow water near the North American coast, they will build up to about 50 metres high, enough to travel several kilometres inland. "There's a significantly broad danger zone," says Day. Although the volcano's unstable flank points directly towards North America, it is not just North Americans who should be worried. Day originally estimated that the collapse would create a shockwave travelling in a straight line across the Atlantic, directly towards America's East Coast. This would happen if the speed of the landslide was faster than the speed of the waves in deep water. But the model shows that the landslide will actually move at around 100 metres per second, about two-thirds as fast as the waves in the water. This means the tsunamis will spread out in an arc. Shallower water near La Palma would then slow the waves down, forcing them to curl around towards northern Africa and northern Europe, even behind La Palma on the Spanish coast." More at Geophysical Research Letters (vol 28, p 3397) -- Tim C. |
#7
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A recent article I read somewhere said that if the predicted bit of
La Palma falls off in one slab the resulting tsunami will lead to the disappearance of the Isles of Scilly (among other damage!) Charlie Pridham writes Lots of people have said that, but it seems unlikely. To create a tsunami requires a high energy shock wave, a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance, although there would certainly be a large wave locally much as when large icebergs break off. I think you confuse speed with energy. If you drop a very very large mass (say 5000 million tons) a few hundred feet (and I think in the case of the canaries it drops a long way down to the ocean floor) then the *energy* released is converted into a (relatively) smaller mass of water travelling *very* fast. I don't know what the conversion factor is but say 1% of the mass travelling at say 20 times the speed would still be quite significant. -- David |
#8
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"Dave" wrote in message ... A recent article I read somewhere said that if the predicted bit of La Palma falls off in one slab the resulting tsunami will lead to the disappearance of the Isles of Scilly (among other damage!) Charlie Pridham writes Lots of people have said that, but it seems unlikely. To create a tsunami requires a high energy shock wave, a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance, although there would certainly be a large wave locally much as when large icebergs break off. I think you confuse speed with energy. If you drop a very very large mass (say 5000 million tons) a few hundred feet (and I think in the case of the canaries it drops a long way down to the ocean floor) then the *energy* released is converted into a (relatively) smaller mass of water travelling *very* fast. I don't know what the conversion factor is but say 1% of the mass travelling at say 20 times the speed would still be quite significant. -- David I may be wrong but I am not confused! :~) once the rock mass was in the water the effect would be slight however far it falls, it can after all only fall and accelerate at 9.81m/s2 . and I still think you would be hard pressed to even detect it in New York were it to happen, (a similar sized lump arriving from space would be travelling at a much higher speed and would indeed cause allsorts of problems were it to hit ocean). The movement of a tectonic plate can in some instances be at very high speed coupled with the total mass on the move gives a huge amount more energy and even then not all underwater quakes produces these waves. -- Charlie, gardening in Cornwall. http://www.roselandhouse.co.uk Holders of National Plant Collection of Clematis viticella (cvs) |
#9
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"Charlie Pridham" wrote in message ... "Dave" wrote in message ... A recent article I read somewhere said that if the predicted bit of La Palma falls off in one slab the resulting tsunami will lead to the disappearance of the Isles of Scilly (among other damage!) Charlie Pridham writes Lots of people have said that, but it seems unlikely. To create a tsunami requires a high energy shock wave, a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance, although there would certainly be a large wave locally much as when large icebergs break off. I think you confuse speed with energy. If you drop a very very large mass (say 5000 million tons) a few hundred feet (and I think in the case of the canaries it drops a long way down to the ocean floor) then the *energy* released is converted into a (relatively) smaller mass of water travelling *very* fast. I don't know what the conversion factor is but say 1% of the mass travelling at say 20 times the speed would still be quite significant. -- David I may be wrong but I am not confused! :~) once the rock mass was in the water the effect would be slight however far it falls, it can after all only fall and accelerate at 9.81m/s2 . That is quite wrong. The rock hits the water quite fast, with a large amount of energy. As it sinks in the water, it gives its enrergy to the water, spreadover a large range in depths. These are just what is neded to excite a deep water wave. and I still think you would be hard pressed to even detect it in New York You could not be more wrong on this issue if you tried. Please desist from making qualitative speculations from the side lines. As has been said before, there are actually model experiments being performed under conditions where the scaling laws are known. The results from those are more important than your wishful thinking. were it to happen, (a similar sized lump arriving from space would be travelling at a much higher speed and would indeed cause allsorts of problems were it to hit ocean). The movement of a tectonic plate can in some instances be at very high speed coupled with the total mass on the move gives a huge amount more energy and even then not all underwater quakes produces these waves. Franz |
#10
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"Charlie Pridham" wrote in message ... "Franz Heymann" wrote in message ... "Sacha" wrote in message k... On 3/1/05 11:30, in article , "Cerumen" wrote: wrote in message ... On Sun, 2 Jan 2005 16:09:33 -0000, "Bob Hobden" wrote: The main risk is the big piece of rock which is expected to fall off an island in the Canaries, generate a tidal wave that will wipe out the East Coats of the USA and not do a lot of good to the low countries. Apparently a tsunami hit the west coast of Ireland in 1775 ? after a seismic event near the Azores and Canaries causing some considerable damage.. A recent article I read somewhere said that if the predicted bit of La Palma falls off in one slab the resulting tsunami will lead to the disappearance of the Isles of Scilly (among other damage!) As well as New York Franz Lots of people have said that, but it seems unlikely. I am afraid that if the whole chunk og rock comes adrift in one go, it is a dead cert. It is only a matter of when. To create a tsunami requires a high energy shock wave, No. That is not so. Any large, localised disturbance will do the trick. a bit of land falling in would, however large not be moving fast enough for the damage to be transmitted any distance, although there would certainly be a large wave locally much as when large icebergs break off. I would rather listen to the physicists who have done the calculations. They actually do know the magnitude of the wave which would occur if the whole cracked chunk of rock fell into the ocean in one go. In a deep ocean with a flat bottom, a tsunami is actually a relatively slow, stately occurrence. All hell begins to break loose when it reaches a sloping shoreline. Franz |
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