Waves Laird Hamilton riding ‘the Wave’ (Riding Giants)

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  • Slide 1
  • Waves Laird Hamilton riding the Wave (Riding Giants)
  • Slide 2
  • Waves When undisturbed by wind (or some other factor such as an earthquake), the sea surface is naturally smooth! Waves are moving energy and begin as a disturbance Wind blowing across the surface of the ocean generates most waves Tides, turbidity currents, coastal landslides, calving icebergs, and sea floor movement can also cause waves
  • Slide 3
  • Waves In an ocean wave, energy is moving at the speed of the wave, but water is not! Waves move energy, with very little movement of particles (including water particles!) The water associated with a wave does not move continuously across the sea surface!
  • Slide 4
  • Imagine a seagull resting on the ocean surface The bird moves in circles up and forward as the tops of the waves move toward its position, and down and backward as tops of the waves move past Energy in the waves flows past the bird, but the gull and its patch of water move only a short distance Each circle is equal in diameter to the wave height
  • Slide 5
  • Orbital Waves As a wave travels, the water passes the energy along by moving in a circular path, called an orbit An wave in which water particles move in closed circles is called an orbital wave Because the wave form moves forward, orbital waves are a type of progressive wave
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  • Orbital Waves The bigger the wave, the larger the size of the orbit The diameter of the orbit diminishes rapidly with depth Wave motion is negligible when orbits reach a diameter that is 1/23 of those at the surface
  • Slide 7
  • Wave motion is negligible below a depth of one half of the wavelength
  • Slide 8
  • Components of a Wave Ocean waves has distinct parts: Wave crest: highest part of the wave above average water level Wave trough: lowest part of the wave below average water level Wave height: the vertical distance between a wave crest and its trough Wavelength: the horizontal distance between 2 successive crests, or troughs
  • Slide 9
  • Slide 10
  • Making Waves Ocean waves are classified by the disturbing force that creates them the extent to which the disturbing force continues to influence the waves once they are formed The restoring force that works to flatten them Their wavelength
  • Slide 11
  • Making Waves Energy that causes waves to form is called a disturbing force Wind blowing across the ocean surface provides the disturbing force to generate capillary waves (waves
  • Making Waves The restoring force seeks to return the water to flatness after a wave has formed in it; gravity provides the restoring force on all waves >1.73cm
  • Slide 13
  • Wavelength is the most useful measure of wave size
  • Slide 14
  • Deep vs. shallow water waves Waves moving through water deeper than their wavelength are deep water waves Example: A wind wave with a 20m wavelength is considered to be a deep water wave so long as it is passing through water >10m deep Waves in water shallower than 1/20 their wavelength are shallow water waves Example: A wave with a 20m wavelength will act as a shallow-water wave if the water is
  • Tsunamis In the open ocean, tsunamis travel at speeds >435 miles per hour Tsunamis in the open ocean have heights of only ~0.5 meters (~1.6 feet)! However, once they approach the shore, they slow in the shallow water and increase in wave height Surges ashore; mistaken for an extremely high tide and so mistakenly called tidal waves
  • Slide 42
  • Abrupt vertical movement along a fault on the sea floor raises or drops water column creating a tsunami that travels from deep to shallow water
  • Slide 43
  • Killer Waves 86% of all tsunamis occur in the Pacific Ocean (Why?) On December 26, 2004, an enormous earthquake struck off the coast of Sumatra in Indonesia Occurred ~19 miles beneath the sea floor near the Sunda Trench, where the Indian Plate is being subducted beneath the Eurasian Plate Ruptured ~750 miles of sea floor!
  • Slide 44
  • Killer Waves This thrusted the seafloor upward, displacing >30 feet of water above it The resulting tsunami spread across the Indian Ocean, literally washing away many coastal villages and causing approximartely 300,000 human deaths in Indonesia (esp. Thailand) and along coastal India and Africa Although much smaller, the tsunami was also detected in the Atlantic, Pacific and Arctic Oceans!
  • Slide 45
  • Indonesian capital of Banda Aceh (before tsunami)
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  • Indonesian capital of Banda Aceh (after tsunami)
  • Slide 47
  • Sequence of photos of tsunami inundating Chedi Resort in Phuket, Thailand on December 26, 2004