Chapt11_TsunamiSeichesTides

Chapt11_TsunamiSeichesTides - Tsunami, Seiches and Tides...

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Tsunami, Seiches and Tides Chap 11
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Other Waves The waves discussed so far, seas, swell and  breakers, are all types of  progressive   waves.  Progressive waves progress: they move from  one place to another.  We have three more types of wave that  doesn't progress, but just moves up and  down in more or less the same place.
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 Other Waves 1. Internal Waves 2. Tsunamis 3. Standing Waves 4. Seiches
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1. Internal Waves Internal waves are  waves that occur not at  the surface of the  ocean, but within the  ocean water.  These generally occur  at a pycnocline, where  surface waters do not  mix with deep waters.  
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Because the density difference  between surface water and deep water  is not nearly as great as the density  difference between wind and surface  water, internal waves are slower than surface waves can have very large wave heights have very long wave lengths
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The large wave heights and slow movements  suggest the pycnocline is actually a wavy  surface that undulates slowly. You've probably seen internal wave devices  in stores that are sold as gifts for desks.  Periods for the real thing are typically  minutes (5-10), whereas periods for surface  waves are usually in seconds. 
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Perhaps the most significant internal wave  occurs in estuaries, where a river meets the  sea.  Fresh water pours into the ocean from the  river, and, being less dense, spreads over  the surface of the ocean as floating,  freshwater.  Internal waves help mix this light, fresh water  with the denser salt water beneath. http://www.youtube.com/watch?v=dECC_L1Tkdk http://www.youtube.com/watch?v=zHId82eT6uM
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Rogue Waves Waves can  constructively interfere , and  grow even bigger by  gaining energy from  ocean currents The result is a huge  rogue  wave. (p.244) Seafarers call these 'freak waves'.  They appear to arise out of nowhere, for the  winds that generated them are not nearby.  A ship cannot take a rogue wave broadside,  as the wave can flip the ship upside-down  (the ship 'rolls over').
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Normally, ships head into waves, so that the  bow (front) of the ship faces the oncoming  crests at more-or-less a right angle.  This minimizes roll (roll causes most  seasickness) and maximizes 'pitch' of the  ship.  But when a rogue wave arrives, the ship  facing such a wave head-on will ride to the  top of the wave.
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The middle of the ship (mid-ships) may  be supported by the wave while the  bow and stern hang out in space,  unsupported.  The result: the ship cracks in two.  It sinks rapidly.  http://www.youtube.com/watch?v=ZyA_O85X-WQ http://www.youtube.com/watch?v=szk83cONAqM
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Chapt11_TsunamiSeichesTides - Tsunami, Seiches and Tides...

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