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# 009-Waves - Wave characteristics and terminology Crest...

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Wave characteristics and terminology Wavelength ( L ) Still water level Orbital motion Crest Trough Wave height ( H )
Wave characteristics and terminology (continued) If wave steepness exceeds 1 / 7 , the wave breaks Period ( T ) = the time it takes one full wave— one wavelength—to pass a fixed position ) ( wavelength ) ( height wave steepness Wave L H = T f 1 ) ( Frequency =

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Calm water Orbital size decreases with depth to zero at wave base Depth of wave base = ½ wavelength, measured from still water level

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Deep- and shallow-water waves Deep-water waves Water depth > wave base Shallow-water waves Water depth < 1 / 20 of wavelength Transitional waves Water depth < wave base but also > 1 / 20 of wavelength Figure 8-6a & b
Wave speed (S) General formula: Deep-water waves: Wave speed ( S ) in meters per second = 1.56 T in seconds Wave speed ( S ) in feet per second = 5.12 T in seconds Shallow-water waves: ( d = water depth) ) ( period ) ( wavelength ) ( speed Wave T L S = meters in 3.13 second per meters in ) ( speed Wave d S = feet in 5.67 second per feet in ) ( speed Wave d S =

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Ocean waves can be classified in various ways: Disturbing Force - the forces which generate the waves. 1. Meteorological forcing (wind, air pressure); sea and swell belong to this category. 2. Earthquakes ; they generate tsunamis, which are shallow water or long waves. 3. Tides (astronomical forcing); they are always shallow water or long waves. Wave Classification
The “sea” and swell Waves originate in a sea ” area Swell describes waves that: Have traveled out of their area of origination Exhibit a uniform and symmetrical shape Figure 8-9

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August 29, 2005 Hurricane Katrina Hurricane Iniki September 1992
"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 Tsunami terminology Often called “tidal waves” but have nothing to do with the tides Japanese term meaning “harbor wave” Also called “seismic sea waves” Created by movement of the ocean floor by: Underwater fault movement Underwater avalanches Underwater volcanic eruptions

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Most tsunami originate from underwater fault movement Figure 8-21a
Fault displacement under water displaces water, water moves to fill vacuum, generating large waves.

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