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waves do not move horizontally , but remain stationary , « trapped » so
to speak , as water moves beneath them.
Other types of progressive waves :
There are other types of progressive waves . The first – an internal
wave- occurs underwater and not at the surface , such waves move
along the pycnoclines , which are surfaces that separate water masses of
different densities. This is analogous to ocean swell which forms at the
contact between two fluids –air and water- where there is a sharp density
discontinuity .
The second the Tsunami , is a series of seismic sea waves that have
nothing to do with tides despite their familiar name of « Tidal waves ».
Internal waves :
Internal waves travel at much slower speeds than do surface waves ,
because the difference in density between two water masses is much less
than it is between air and water . However , their physical size can be
much grander than ocean swell. For example , the periods of internal
waves are measured in minutes , rather than in seconds , and their
wavelength in hundreds rather than in tens of meters . Furthermore
,although they characteristically have heights on the order of several
meters , the larger internal waves can attain and even exceed the height
of 100 meters –almost three times higher than some of the larger rogue
waves created by consecutive wave interference at the sea surface .
Tsunamis :
In earlier times , seismic ocean waves were called Tidal waves ,
incorrectly implying that they were related to tides. To eliminate this
confusion , scientists worldwide
decided to use the Japenese word
Tsunami to refer to seismic ocean waves.
Because of wave-lengths greater than 100 kilometers , waves in a
tsunami are shallow-water waves over most parts of the ocean , except
over deep-sea trenches , where they are intermediate-water waves.