Waves
• Wave- disturbance caused by the
movement of energy from a source
through a medium (solid, liquid, gas)
– As the energy travels, the medium
moves in specific ways
• In ocean waves, the energy is moving
through the water, but the water is not
moving
Parts of a Wave
• Crest = highest part of the wave
• Trough = lowest part of the wave.
• Wave height = vertical distance
between the trough and the crest.
• Wavelength = the distance between
troughs or crests.
• Period = the time a wave takes to go by
any given point.
Deep Water, Transitional Water
and Shallow Water Waves
• Characteristics of a wave mostly depend
on the depth of the water they are in.
– Deep water waves are in water that is
deeper than about ½ its wavelength
– Transitional waves travel through water
that is between 1/20 and ½ of their
wavelength.
– Shallow water waves are waves in water
shallower than 1/20 their wave length
Wind Waves
• Wind waves are waves caused by wind
blowing across the water
– The faster and the longer the wind blows,
the bigger the waves get.
– The greater the fetch, the distance over
which the wind blows unimpeded, the bigger
the waves get.
Wave Refraction
• Wave Refraction occurs when a wave
line approaches the shore at an angle.
– The line does not break simultaneously.
• The part is shallower water breaks first and then
the deeper parts break.
• So the waves ‘bend’, and can bend as much as
90°
Wave Diffraction
• Wave Diffraction is the propagation of a
wave around an obstacle
– Wave crests excite the water at the gap
which generates new waves.
Internal Waves
• Internal Waves are subsurface waves
that can form between layers of different
densities
– They can be 30 m high with wavelengths
over 0.8 km
– They move very slowly because the
difference in density is small
– May be important in mixing nutrients and
can be quite powerful.
Storm Surge
• Storm Surges
– Technically not a wave because it is only a
crest
– Low pressure in the atmosphere causes
water to dome, which can be as high as 9 m
– Can have devastating consequences
because they are often combined with high
wind waves
Seiche
• Seiches
– Like the water in a bath tub, confined bodies
of water will rock back and forth sometimes
due to atmospheric conditions or seismic
activity
Tsunami
• Tsunami- Japanese term meaning
‘harbor wave’
– Shallow water waves caused by the rapid
displacement of ocean water by landslides,
icebergs, volcanic eruptions or earthquakes
– They have wavelengths up to 200 km and are therefore
never in shallow water
– Move at about 212 m/sec or 470 miles/hour
– Very low steepness and a very long period (5 to 20
minutes)
– Incredibly Destructive
» >200,000 people died on Dec 26, 2004