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Question about tsunami wave

  1. Dec 29, 2004 #1
    Question about tsunami waves

    Do tsunami waves contain huge energy? When waves are traveling in ocean, will fishes die when waves pass through them? If not, why?

    Last edited: Dec 29, 2004
  2. jcsd
  3. Dec 29, 2004 #2


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    http://www.poemsinc.org/oceano/waves.htm#tsunami properties

    "There are two aspects of a disturbance that we need to distinguish: suddenness (velocity, v) and volume (mass, m). The two combined create impulse or impact (v x m), and kinetic energy (v x v x m). Impulse determines how much matter will be moved by the disturbance (water and earth and buildings), which is often more destructive than the energy content of the disturbance. Think for instance of the huge energy contained in normal moon tides, which causes no harm because tides move slowly."

    As regards fish....apparently the animals (elephants, tigers, rabbits..)
    in Sri Lanka near the area of devastation ALL LEFT THE SCENE before
    the tsunami. Go figure.

    Some of us know people in SE asia.

    Kea :frown:
  4. Dec 29, 2004 #3
    Do tsunami waves move very fast in ocean, not like moon tides?

  5. Dec 29, 2004 #4


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    Staff: Mentor

    The energy in the tsunami wave is distributed in huge volumes/masses of water. The pressure doesn't really change. The height of water did not change much out at sea - probably a few meters.

    There were scuba-divers in the water somwhere near Thailand when the tsunami waves passed. They did not feel much, except they noticed the turbidity (suspended solids) increased and the sudden presence of garbage and debris (from nearby land). It was not until they surfaced that they realized that the disaster had happened.

    The damage comes when large volumes of water reach shorelines and hit fixed structures. The waves that were a few meter high grow to 10-15-20 m at the land. I suggest you go to a beach with 2-3 meter high waves, stand in front of one and feel the force from a 'little' wave. Then imagine 10-20 or more times the force.

    Fish caught near the shoreline will probably be killed if they do not escape as the first waves crash on shore.

    Out a sea (deep), the tsunami waves move very fast ~800 km/h (500 mph) in deep ocean, and slower near the continental shelf - shallow oceans or seas - where speed is something like ~500 km/h (300 mph). As the waves approach shoreline, they increase in height and slow in speed.

    The speed depends on the depth of the water - see the following for examples.



    http://electron4.phys.utk.edu/141/dec8/December 8.htm
    Last edited: Dec 29, 2004
  6. Dec 29, 2004 #5
    Thank you so much. Your explanations is really good. :!!)

  7. Dec 29, 2004 #6


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    Science Advisor

    Waves on water have speeds that depend on their wavelength: the longer the wavelength, the faster they travel. You can observe this on a lake. Slow-moving little waves are unchanged by large waves passing through them.
  8. Dec 29, 2004 #7


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    Staff: Mentor

    ...and since moon tides go around the earth in 24 hours, they move at something like 1000mph at the equator.
  9. Dec 29, 2004 #8


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    The felt it alright, while in the water, they were shot down 45 feet, then back up again to their original position. At this point the water became murky because the sea floor was so disturbed. One of the scuba divers was new to it, but her instructor knew immediately that it wasn't a normal underwater current.

    When the surfaced, a boat picked them up and took them to a different area as the nearby hotel no longer existed.

    Unlike large waves (Hawaii recently had some 40 foot waves), tsunamis have a huge length, so it's like a small part of the ocean has risen up, and the tsunamis travel well past the beach inland bringing huge amounts of water.
  10. Dec 30, 2004 #9
    I heard the tsunami affected the period of earth's rotation? Can someone explain how this happened? My only guess was something to do with conservation of angular momentum.
  11. Dec 30, 2004 #10


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    Thanks for your comment Jeff - point taken - but I was thinking in terms of pressure pulses or something like mild 'shock waves' rather than motion of currents. Of course, near the shore line, one could be lifted upward then slammed into the sand or sea floor.

    In fact, I heard an interview with some divers who were off the coast of Thailand, and several said they did not notice anything. Then the dive leader gathered them and took them to the surface, and that's when they new something serious had happened. I don't know if it was the same group to which you refer.
    Last edited: Dec 30, 2004
  12. Dec 30, 2004 #11


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    Just a pair of divers, one was a girl just learning to scuba dive, so she really didn't know that it was unusual. Her dive instructor did. This article was in the Orange County (California) Register, because the girl lives in this area.
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