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Wind Driven Waves and

TsunamisZack & Garry

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Wind Driven Waves

From traveling 1000s of km acrossthe ocean, or the ripples in a smallpuddle.

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How they form

Far away from our shores, oceanicwinds pass over large stretches ofopen ocean.

Friction and pressure transfer theenergy of the wind to the top-mostlayers of the water.

The resulting disturbance istransferred through the water until itcrests and hits land.

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What is a wave? There is some movement of the water, but

for the most part it acts as the medium inwhich the energetic disturbance is

transferred. Wave: "a disturbance or variation that

transfers energy progressively from pointto point in a medium and that may take theform of an elastic deformation or of avariation of pressure, electric or magneticintensity, electric potential, ortemperature."

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An important difference

The waves which cause the regulartidal cycles are caused by thegravitational pull of the moon and theearths rotational properties.

They are not caused by the wind.

Tidal waves are a movement of the

oceans water, whereas wind drivenwaves are the transfer of energy(disturbance) through the medium.

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Wind sea: When waves are beinggenerated and effected by a local

system.

Swell: The wave which remains after

the generating wind ceases to affectit. Ie: the wave has traveled manymiles from its origin.

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Waves are characterized by: 1) The height of the wave.

2) The distance between crests

(wavelength). 3) The direction the wave travels

(wave propagation).

4) The time between consecutivecrests (wave period).

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Wave properties are dependant on: 1) Wind speed (more energy

transferred).

2) Fetch length (the distance that thewind drags along the sea to transferenergy).

3) The width of the fetch area.

4)The duration that the wind asblown on the fetch.

5) The depth of the water.

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Types of wind driven waves. 1) Ripples: are small and short lived,

do not persist if the wind stops.

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Types of wind driven waves. 2) Seas: Form under sustained winds

and can be erratic in motion. Much

larger version of ripples. Can remainafter the wind has stopped.

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Types of wind driven waves. 3) Swells: What we see breaking on the

shore. As seas propagate from where theywere formed, they go in their own

directions. They sort based on direction andwavelength, toward distant shores.

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Tsunamis A tsunami is a series of water waves caused by

the displacement of a large volume of a bodyof water, usually an ocean, though it can occur

in large lakes. Tsunamis can devastate coastal regions by two

mechanisms: the smashing force of a wall ofwater travelling at high speed, and thedestructive power of a large volume of waterdraining off the land and carrying much debriswith it.

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Tsunami in Newfoundland On 18 November 1929 a tsunami struck

Newfoundland's Burin Peninsula and causedconsiderable loss of life and property.

Giant waves hit the coast at 40 km/hour,flooding dozens of communities and washingentire homes out to sea.

The disaster killed 28 people and left hundreds

more homeless or destitute.

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Causes of Tsunamis Earthquakes, volcanic eruptions and other

underwater explosions (including detonationsof underwater nuclear devices), landslides,

glacier calvings (the sudden release andbreaking away of a mass of ice from a glacier,iceberg, ice front, ice shelf or crevasse),meteorite ocean impacts, and otherdisturbances above or below water all have the

potential to generate a tsunami. About 80% of tsunamis occur in the Pacific

Ocean, but they are possible wherever thereare large bodies of water, including lakes

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Tsunami reaching the shore If the first part of a tsunami to reach land is a

troughcalled a drawbackrather than a wavecrest, the water along the shoreline recedes

dramatically, exposing normally submergedareas.

When the wave enters shallow water, it slowsdown and its amplitude (height) increases. (itswavelength decreases).

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Revisions Shear: Transfer force between two fluids

(air/wind or liquid).

Wave velocity is proportional to wavesize.

Depth is important because below adepth below wavelength, the wave

becomes elliptical and breaks due to thetop having less friction than the bottomand being pushed further ahead.

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Fetch