Waves

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Waves
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• Description of Waves
• The simplest way of looking at waves is the
  concept of a wave as a harmonic oscillation. It
  can then be described by its
• period t the time it takes 2 successive wave
  crests to pass a fixed point
• frequency w 1 / t the number of waves passing
  a fixed point per second
• wavelength l horizontal distance between two
  successive wave crests
• wave speed c l / t
• wave height H 2A (A amplitude) vertical
  distance between wave crest and adjacent trough
• wave steepness d H / l

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Calm water
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Wave Classification

• Ocean waves can be classified in various ways
• Disturbing Force- the forces which generate the
  waves.
• Meteorological forcing (wind, air pressure) sea
  and swell belong to this category.
• Earthquakes they generate tsunamis, which are
  shallow water or long waves.
• Tides (astronomical forcing) they are always
  shallow water or long waves.

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Hurricane Andrew- 1992
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"Tsunami" - a Japanese word meaning "great wave
in harbor". It is a series of ocean waves
commonly caused by violent movement of the sea
floor by submarine faulting, landslides, or
volcanic activity. A tsunami travels at the speed
of nearly 500 miles per hour outward from the
site of the violent movement.
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Tsunami

Fault displacement under water displaces water,
water moves to fill vacuum, generating large
waves.
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Maui Puunene AvenueAftermath of a Tsunami in
Kahului, 1960
Tsunamis struck Kahului in 1946, 1957, 1960, and
1964. The earliest historically recorded tsunami
in Kahului occurred on November 7, 1837, when a
large tsunami traveled 800 yards inland and
destroyed a Hawaiian village.The 1960 tsunami
was caused by a violent earthquake in Chile on
May 22, 1960. It took approximately 15 hours for
the tsunami to travel from Chile to the Hawaiian
Islands. The tsunami killed 61 people in Hilo on
the Big Island, but there were no other human
casualties on any of the other islands. The
tsunami caused moderate damage in Kahului.
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A giant wave engulfs the Hilo pier during the
1946 tsunami. The red arrow points to a man who
was swept away seconds later.
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tides w/out tsunami
Earthquake originated in Anchorage, AK
Passage of a tsunami as seen in a sea level
record from Hilo, Hawaii. The observed sea level
shows high frequency variations with a period of
approximately 20 minutes and an initial amplitude
of nearly two meters (total tsunami wave height
3.7 m)
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This mathematical simulation (above) shows the
tsunami created by the Cascadia Subduction Zone
earthquake on January 26, 1700, as it reaches
Hawaii on its way across the Pacific Ocean (5
hrs).
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• Free Waves, Forced Waves
• Free waves- a wave that is formed by a disturbing
  force such as a storm. Waves continue to move
  without additional wind energy
• Forced wave- a wave that is maintained by its
  disturbing force, e.g., tides

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• Restoring Force
• Force necessary to restore the water surface to
  flatness after a wave has formed in it
• Capillary waves- wavelength lt 1.73 cm
• Gravity waves- wavelength gt 1.73 cm

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Deep-water, Transitional, Shallow-water
waves Wavelength- determines the size of the
orbits of water molecules within a wave Water
depth- determines the shape of the
orbits Deep-water waves- more circular
orbits Water Depth ? 1/2 of wavelength Transitiona
l waves- intermediate-shaped orbits 1/20
wavelength ? depth ? ½ wavelength Shallow-water
waves- orbits are more flattened Water Depth ?
1/20 of wavelength
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• Wind Waves- gravity waves formed by the transfer
  of wind energy into water
• Wave ht- usually lt3m
• Wave length- 60-150m
• Factors that affect wind wave development
• Wind strength
• Wind duration
• Fetch- the uninterrupted distance the wind blows

http//www.newportsurf.com/tides.html
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Interference and Rogue Waves
Interference waves when waves from different
storm systems overtake one another. They add
(constructive interference) or subtract
(destructive interference) from the other.
Constructive
Destructive
Mixed
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• Rogue waves
• freak waves that come out of nowhere
• created by constructive interference
• formed by the interaction of a wind wave and a
  swift surface current
• common in southeastern tip of Africa

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Waves approaching shore

• Types of Breaking Waves
• Plunging breaker
• Spilling breaker
• Surging breaker
• Factors that determine the position and nature of
  the breaking wave
• Slope
• Contour
• Composition

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a gradual sloping bottom generates a milder wave
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Surging Breaker

• doesn't break, because it never reaches critical
  wave steepness
• breaker diminishes in size and looses momentum
• Found on beach with a very steep or near vertical
  slope

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Sunset Beach
Waikiki
What type wave are these?
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Wave Refraction- when a wave approaches an
inclined surface (shore) from an angle, the wave
slows and bends, paralleling the shoreline,
creating odd surf patterns
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Wave Diffraction- Propagation of a wave around an
obstacle


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Wave Reflection- a progressive wave striking a
vertical barrier and being reflected in the
direction from where they came
The Wedge, Newport Harbor, Ca
waves
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Rip Current
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Internal Waves- at thermocline/pycnocline layer
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Wave exposed environment

• constant coral species turnover associated with
  mortality
• and recruitment
• rarely thicker than a single coral colony

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Mortality on wave exposed environment due to

• Breakage
• Scour
• Abrasion

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Depth- lack of coral accretion in shallow open
ocean coastline due to wave energy Absence of
mature barrier reef in Hawaiian Islands
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Wave climate in Hawaii

• 5 types of open ocean swells that cause
  disturbance to coral
• Destructive waves-causes high mortality on reef
  building corals
• North Pacific winter waves on north and western
  coastline
• hurricane generated swells on south or southwest
  coastline (40 yr cycle)

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Low moderate nondestructive waves- optimizes
mixing and nutrient uptake or exchange, usually
beneficial due to increased circulation and
nutrients between water and organisms 3.
Tradewinds generated from northeast or east ht.
of 1-3 m, occurs 90 of summertime and 55-65 of
wintertime 4. Long period southerly swell from
southern ocean during the Austral winter common
between April and September (1-2 m in ht) 5.
Kona storm generated waves (4m) occasionally
may be destructive and cause beach and shoreline
erosion 
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Reef Front in a Low Energy Environment
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Reef Front in a High Energy Environment
Algal Ridge
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Upper Reef Slope of a High Energy Environment
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Upper Reef Slope
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Upper Reef Slope of a Lower Energy Environment
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Table 1. Community structure and growth of coral
reef at sites selected for study. Attributes of
community structure are based on one 50 m
transect at each station. Annual coral growth
rates are averages of 10 colonies.