- Ocean waves have characteristics that can be measured and used
to describe each wave. Among the most useful of these are wave
height and wavelength. Wave height is the vertical distance between
wave crest (the highest point of each wave) and wave trough (the
lowest point of each wave). Wavelength is the horizontal distance
between any two successive wave crests (or wave troughs). Refer
to the Wave Characteristics Diagram and
circle the letter below which indicates each of the following
- Using the scale at the base of the diagram, measure the wavelength
of the wind-generated wave in the diagram and record it in the
Wave Characteristics Table in the column
- Ocean waves are also described in terms of wave period. This
is the time required for two successive crests (one wavelength)
to pass a fixed point. On the ocean, it may be easier and more
accurate to record how long it takes ten waves to pass and then
divide by ten to obtain the average period. If it takes 100 seconds
for 10 of the above wind-generated waves to pass, deter-mine the
period and record it in the table.
- An ocean wave is also characterized by wave speed, or the distance
it travels divided by the time it takes to travel that distance.
Having already determined the time it takes the above wind-generated
wave to travel a distance of one wavelength (the wave period),
determine the wave speed by dividing the wavelength by the wave
period. Record the wave speed and circle the generating factor
in the table.
- Tides can be thought of as global-scale ocean waves generated
by gravitational attraction of the Moon and Sun. High tide is
the crest of the wave and low tide the trough. Where two high
tides occur each day, the wave period is about 12.5 hours. If
the wavelength is about 20,000 km (half the circumference of Earth),
determine the wave speed as above and record all three wave char-acteristics
and circle the generating factor in the table.
- Tsunamis, sometimes erroneously called tidal waves, are ocean
waves generated by earthquakes and submarine landslides. They
have a period of about 0.5 hour and a wavelength of about 200
km. Again, determine the wave speed as above and record all three
characteristics and circle the generating factor in the table.
- Although the speed of a tsunami is influenced by its interaction
with the ocean bottom, using the speed you calculated, it would
take about (one hour) (ten hours) (1 day) for a tsunami triggered
by a coastal earthquake in Alaska to travel to Hawaii (a distance
of 4,000 km).
- From what you have learned about the factors that generate ocean
waves, why is the term "tidal wave" not an accurate
term when referring to a tsunami?