Don't want to pollute the other thread as it were.
How would a ship at sea fare in a tsunami ?
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It would not notice it pass if it were out in the open ocean. A mere ripple on the surface.
John
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The wavelength is very long out at sea, ships are rarely sunk in deep water by Tsunami.
The shallows are a different matter.
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If it was in deep water well offshore it would not even notice it, it is only a gradual raising of the sea level. It is only when the wave reaches shallow water and has nowhere to go but upwards as it moves forwards it gets dangerous. This is how surfing waves work.
Last edited by: Old Navy on Sun 13 Mar 11 at 20:46
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See science.howstuffworks.com/nature/natural-disasters/tsunami4.htm
which describes a tsunami as not a wave but as energy moving through the water. More or less, apologies for para-phrasing.
John
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Brings us nicely onto the Rogue Wave.
en.wikipedia.org/wiki/Rogue_wave
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>> Brings us nicely onto the Rogue Wave.
>>
As said in your link, Nothing more mysterious than several waves combining, It happens all the time, it is just the scale of them that makes a difference. If it is seriously rough anyway a few combining can make a monster, most are never seen. A monster wave and a ship being in the same place at the same time is a rare event.
Last edited by: Old Navy on Sun 13 Mar 11 at 21:28
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A monster wave and a ship being in the same place at the same time is a rare event.
Makes sense - probably the same theory as the "big sky" on in aviation - i.e. a collision is unlikely to occur given the 2D size of the place.......
Thanks for the info on the Tsunami thing - just a random thought thing.
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"a collision is unlikely to occur given the 2D size of the place......."
You'd get a few over Heathrow though on that theory.
John
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I remember the company I worked for slicing through its N. Sea production platforms, jacking them up and inserting extra bits to raise them higher above sea level. partly because of this, partly becasue the sea bed was sinking due to the extraction of oil. Measuring sea level was 'arder then back inthe 80s, they didn't have GPS and satellites recording such things.
If anyone is having difficulty thinking of wave energy, rhink of a Newton's Cradle. Energy passes through with almost no movement of the middle balls. But the one at the end (the coast) unconstrained by further balls, releases the energy.
John
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like others have said its an energy wave in the ocean in deep water but as it shallows the energy lifts the water into a water wave.
a bit simplistic description of me but i think its about right
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Although waves on water are the way most people think of waves, the relationship between the visible wave crests and the transport of energy is quite complicated.
In the much simpler case of a typical sound wave in air, the energy travels at the same speed as the wave front.
In water waves, that isn't the case. The energy is transported by a wave group or packet. Individual wave fronts may enter and leave the wave group - at the front edge if the wave speed is faster than the group speed.
To see this, pitch a stone into a still pond, and watch any individual wave front - it will seem to disappear, but other waves will also re-appear at the other end of the group or packet.
This group velocity effect is a result of the waves being dispersive, where different frequencies (or equivalently different wavelengths) travel at different speeds.
If sound waves were dispersive, comprehensible speech and music simply couldn't travel any distance, the frequencies would seperate out.
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Ocean waves are elliptical, I assure you that being a few hundred feet under the surface of the Atlantic in a storm is most unpleasant, though not as bad as being on the surface.
Last edited by: Old Navy on Sun 13 Mar 11 at 22:06
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>> Ocean waves are elliptical, I assure you that being a few hundred feet under the
>> surface of the Atlantic in a storm is most unpleasant, though not as bad as
>> being on the surface.
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In addition,
It is the bottom of these ellipses running into shallow water that causes breakers to form on a beach, as poorly described above. The wave peaks and troughs seen in open oceans are just the top of vertical water movement that goes down many hundreds of feet.
Last edited by: Old Navy on Sun 13 Mar 11 at 22:51
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>> as poorly described above. >>
I should have added "by me" to the above. :-)
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So a submarine running in shallowish water near the coast is not a good idea........
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Specially the Japanese coast.
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>> Specially the Japanese coast.
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You are out of your depth Z. :-)
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>> Specially the Japanese coast.
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and a nuclear submarine.
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>> So a submarine running in shallowish water near the coast is not a good idea........
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Maintaining depth accurately is not normally a problem, what can cause problems when close inshore is fresh water runoff which changes the specific gravity of the water unpredictably and this requires the weight of the submarine to be changed rapidly to maintain depth.
Last edited by: Old Navy on Sun 13 Mar 11 at 23:12
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Going back to the OP, I remember in that programme where they re-enacted (if thats the right word!) the Krakatoa disaster they showed the ship being steered into the wave that created, which i assume would have been classed as a tsunami? Looked pretty rough!
Last edited by: hobby on Mon 14 Mar 11 at 13:28
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>> Going back to the OP, I remember in that programme where they re-enacted >>
Dont believe all you see in a programme, its probably 90% fiction. Having said that heading slowly into big waves is the safest option. I the waves are big enough or the boat / ship is small enough it dosen't make any difference, you are going down.
Last edited by: Old Navy on Mon 14 Mar 11 at 13:38
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Yes, I did think that, but it was supposed to be based on the ships log and Captains' account of the incident so thought that there may be some truth behind it... It certainly looked terrifying enough...
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Your in trouble when the wave length (distance from tip to tip) is longer than the thing its trying to hit. It means all you can be in the trough and all of the peak can be above you.
The navy has been battling the "long and thin" or "short and fat" ship argument for ages.
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I read somewhere that, in the middle of an ocean, a tsunami type wave would pass very quickly and only be a matter of inches high. As it gets closer to land it slows down and builds up. Evidence was found in Alsaka indicating that a wave over 67 metres high had hit it, in Shoup Bay in 1964
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"Based on this description, it is possible that the quake had caused the entire glacier (or a large portion of it) to slide over the cliff. What the fisherman may have seen, therefore, could have been that section breaking off and falling into the bay. This might account for the vast displacement of water, while leaving little or no evidence once the ice melted. The height of the wave, however, was accurately measured at 1,720 feet (520 m), based on the elevation extent of the damage caused to the foliage up the headlands around the bay."
Full link here (Wiki)
en.wikipedia.org/wiki/1958_Lituya_Bay_megatsunami
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A general tsunami question. - Tooslow
