WavesWaves

One of the major deities in Greek mythology, Poseidon was the supreme ruler of the seas. The Romans called him Neptune. An awesome, unruly, and powerful god, Poseidon was associated with storms, earthquakes, and some other violent forces of nature. When angry, he could stir the sea to a fury. But he could also calm the raging waters with just a glance. One of his titles, Enosichthon (Earth-shaker), reflected his ability to cause earthquakes by striking the earth and mountains with his trident. Another name for Poseidon was Hippios (lord of horses), and the god presented horses as gifts to various individuals. Poseidon rode the waves in a swift chariot drawn by golden sea horses. He used his mighty trident not only to provoke earthquakes and stir ocean waves but also to raise new land from beneath the sea or cause existing land to sink below the waters. Although often helpful to humans—protecting sailors at sea, guiding ships to safety, and filling nets with fish—Neptune could be a terrifying figure as well. Quick to anger, he directed his fury at anyone who acted against him or failed to show proper respect.

Read more: http://www.mythencyclopedia.com/Pa-Pr/Poseidon.html#ixzz1dKdjjyn0

Neptune's Horses by Walter Crane of 1892

WavesWaves

• Transport energy over a body of waterTransport energy over a body of water

• Can cause coastal erosionCan cause coastal erosion

WavesWaves Origin and TypeOrigin and Type

•Wind waves – “wind-generated”Wind waves – “wind-generated”

• Seiche – “pressure-generated”Seiche – “pressure-generated”• Tsunami – “seismic-generated”Tsunami – “seismic-generated”• Tide – “gravity-generated”Tide – “gravity-generated”

Wave TerminologyWave Terminology

•Still water line – level of ocean if it were flat w/o wavesStill water line – level of ocean if it were flat w/o waves• Crest – highest part of waveCrest – highest part of wave• Trough – lowest part of waveTrough – lowest part of wave

• Amplitude – distance between crest and still water lineAmplitude – distance between crest and still water line• Wave height (H) – vertical distance between crest and troughWave height (H) – vertical distance between crest and trough

• Wavelength (L) – horizontal distance from each crest or each Wavelength (L) – horizontal distance from each crest or each troughtrough

– ½ the wave height½ the wave height

– Or any point with the same successive pointOr any point with the same successive point

Still water lineHeight

• Steepness = Height (H)/length (L)Steepness = Height (H)/length (L)

Wave ParametersWave Parameters

•Period (T) – the time it takes for two successive Period (T) – the time it takes for two successive waves to pass a particular pointwaves to pass a particular point

• Frequency (f) – the # of waves that pass a Frequency (f) – the # of waves that pass a particular point in any given time periodparticular point in any given time period

Deep Water WaveDeep Water WaveMotionMotion

•Water particles move in orbitsWater particles move in orbits

• Particle motion ceases at ½ Particle motion ceases at ½ wavelengthwavelength

• Diameter of orbits decrease with Diameter of orbits decrease with depthdepth

• Waves transmit energy, not water massWaves transmit energy, not water mass

Waves Waves TypesTypes

• Deep WaterDeep Water

•Shallow WaterShallow Water

– HH22O depth is >1/2 O depth is >1/2 wavelengthwavelength

– Depth is <1/20 Depth is <1/20 wavelengthwavelength

Orbital MotionOrbital Motion

• When under a wave crestWhen under a wave crest– Water moves up and Water moves up and

forwardforward

• When under a troughWhen under a trough– Water moves down Water moves down

and backand back

• Thus, water particles do Thus, water particles do not move forwardnot move forward– They move in circlesThey move in circles

WavesWavesVelocityVelocity

•The longer the wavelength, the faster the wave travelsThe longer the wavelength, the faster the wave travels

• Velocity (V) = wavelength (L)/Period (T)Velocity (V) = wavelength (L)/Period (T)• For example:For example:– If T= 10 sec; L = 100 mIf T= 10 sec; L = 100 m

– Then 100 m/10 sec. = 10 m/secThen 100 m/10 sec. = 10 m/sec

WavesWavesGenerationGeneration

•Generated by Force Generated by Force

– Sea Wrinkles Sea Wrinkles ripples ripples wind waves wind waves swells swells

• Generated at storm centersGenerated at storm centers

• Separation of waves by Separation of waves by differing rates of travel - differing rates of travel - dispersiondispersion

– wind or airwind or air

WavesWavesSizeSize

•Factors determining size:Factors determining size:º FetchFetch

º Wind velocityWind velocity

º DurationDuration

– Distance wind blows over open oceanDistance wind blows over open ocean

– Speed of windSpeed of wind

– Length of time wind blowsLength of time wind blows

WavesWavesDispersionDispersion

•Wave train – a set of waves Wave train – a set of waves with the same wavelengthwith the same wavelength

• Individual waves move Individual waves move faster than wave trainfaster than wave train– wave dies out at front of wave dies out at front of

train while new waves form train while new waves form at rearat rear

• Wave train travels half Wave train travels half the speed of individual the speed of individual wavewave

Wave InterferenceWave Interference

•Combination of wavesCombination of waves– Build from one another = ConstructiveBuild from one another = Constructive

– Cancel each other = DestructiveCancel each other = Destructive

Shallow Water WavesShallow Water Waves

3. Orbits progressively flatten at depth3. Orbits progressively flatten at depth

6. Just above seafloor particles move in back-and-forth motion6. Just above seafloor particles move in back-and-forth motion

4. Wave height (H) increases and wavelength (L) decreases4. Wave height (H) increases and wavelength (L) decreases

1. Swell feels bottom at depth < ½ wavelength1. Swell feels bottom at depth < ½ wavelength2. Wave crest peaks and wave slows2. Wave crest peaks and wave slows

5. Wave breaks when H/L ratio > 1/75. Wave breaks when H/L ratio > 1/7

Breaking WavesBreaking Waves

Breaking wavesBreaking wavesTypesTypes

•Depends on steepnessDepends on steepness

• Type of Breakers:Type of Breakers:

(a) Spilling(a) Spilling

(b) Plunging(b) Plunging

(c) Surging(c) Surging

– Gentle slopesGentle slopes

– Rolls onto beachRolls onto beach

– Surf gently rolls Surf gently rolls over the frontover the front

– Moderately steep slopeModerately steep slope

–Wave curls forming Wave curls forming a tunnela tunnel

– Steep slopeSteep slope

WavesWavesCharacteristicsCharacteristics

•RefractionRefraction– Bending of wavesBending of waves– Waves approach shore at angle and dragsWaves approach shore at angle and drags

– Feels bottom first and slowsFeels bottom first and slows• DiffractionDiffraction– As waves pass through small opening, waves spreadAs waves pass through small opening, waves spread

SeichesSeiches

•Standing wave oscillatesStanding wave oscillates

• Stationary point (node)Stationary point (node)

• Occurs in enclosed basins and/or lakesOccurs in enclosed basins and/or lakes

• Rise and fall of water levelRise and fall of water level

TsunamisTsunamis

•Giant sea waves generated by earthquakesGiant sea waves generated by earthquakes

TsunamiTsunamiCausesCauses

•EarthquakeEarthquake

• VolcanoesVolcanoes

• LandslidesLandslides

• Meteor impactMeteor impact

TsunamiTsunamiCharacteristicsCharacteristics

•Shallow water waveShallow water wave

• Energy passes through Energy passes through entire water columnentire water column

• Long periods (T)Long periods (T)

• long wavelengths (L)long wavelengths (L)

• Travel at great speedsTravel at great speeds

• Deep wave baseDeep wave base

– T = 10-20 min.T = 10-20 min.

– L = 100-200 kmL = 100-200 km

– c = 200 m/sc = 200 m/s

• Small Height (H)Small Height (H)–H = 1-2 mH = 1-2 m

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Earthquake-Generated Earthquake-Generated TsunamiTsunami• Usually associated with subduction zonesUsually associated with subduction zones

– Water is displaced suddenlyWater is displaced suddenly

TsunamiTsunamiCrest and TroughCrest and Trough

Historical TsunamisHistorical Tsunamis1883 Krakatau1883 Krakatau

•Explosive volcanoExplosive volcano

•Large landmasses fell into the oceanLarge landmasses fell into the ocean

•36,000 people killed by tsunami36,000 people killed by tsunami

Today

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Earthquake-Generated Earthquake-Generated TsunamiTsunami

• Chile, South America (1960)Chile, South America (1960)– 9.5M, largest EQ ever recorded9.5M, largest EQ ever recorded– 33rdrd wave 11 m (30’) high; 1 hour period wave 11 m (30’) high; 1 hour period– 909 died; 834 missing909 died; 834 missing– Tsunami Warning System in placeTsunami Warning System in place

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Lessons from ChileLessons from Chile

• HawaiiHawaii– 61 died61 died

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Chile, 1960Chile, 1960

• JapanJapan– 181 deaths181 deaths

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Landslide-Generated Landslide-Generated TsunamiTsunami• As large mass of land falls into ocean, a huge volume As large mass of land falls into ocean, a huge volume of water is displacedof water is displaced

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Landslide-Generated Landslide-Generated TsubnamiTsubnami• Lituya Bay, Alaska (1958)Lituya Bay, Alaska (1958)

– 150-m high wave150-m high wave– Stripped vegetationStripped vegetation– Ancient tree trim shows Ancient tree trim shows

previous occurrenceprevious occurrence

Historical TsunamisHistorical Tsunamis1946 Pacific Tsunami1946 Pacific Tsunami

•Aleutian Island EarthquakeAleutian Island Earthquake•Killed 165 people in HawaiiKilled 165 people in Hawaii•Resulted in the creation of Resulted in the creation of

the 1the 1stst “tsunami warning “tsunami warning system”system”

Historical TsunamisHistorical Tsunamis2004 Indonesian Tsunami2004 Indonesian Tsunami

•9.0 M earthquake9.0 M earthquake

•Deadliest tsunami ever Deadliest tsunami ever recordedrecorded

•>260,000 people killed>260,000 people killed

Japan TsunamiJapan Tsunami

• Tsunami – The Great WaveTsunami – The Great Wave

• Aerial View of Japan TsunamiAerial View of Japan Tsunami

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Tsunami DangersTsunami Dangers

DrowningDrowning

Severe abrasion by draggingSevere abrasion by dragging

Thrown against solid objectsThrown against solid objects

Carried out to sea in outgoing waveCarried out to sea in outgoing wave

Hit by debrisHit by debrisHouse, cars, trees, rocksHouse, cars, trees, rocks

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Tsunami Hazard MitigationTsunami Hazard Mitigation

• Land Use ZoningLand Use Zoning

– Build to elevations above flood potentialBuild to elevations above flood potential

– Structures engineered to resist erosion and Structures engineered to resist erosion and scourscour

– Streets and buildings built perpendicular to Streets and buildings built perpendicular to shoreshore

– vegetationvegetation

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The Pacific Tsunami Warning SystemThe Pacific Tsunami Warning System

Two StepsTwo Steps1.1. Tsunami WatchTsunami Watch

– Issued when an earthquake > 7.0M is detected in the Pacific Issued when an earthquake > 7.0M is detected in the Pacific OceanOcean

2.2. Tsunami WarningTsunami Warning– Significant Tsunami is identifiedSignificant Tsunami is identified

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Tsunami PredictionTsunami Prediction

• Pressure sensor on Pressure sensor on ocean floor detects ocean floor detects changes in wave changes in wave heightheight

• Transmit signal via Transmit signal via satellitesatellite

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Surviving a TsunamiSurviving a Tsunami

1.1. If you feel an EQ when near the coast, get to high If you feel an EQ when near the coast, get to high groundground

2.2. Do not return to shore after initial waveDo not return to shore after initial wave

3.3. Never go to the shore to watch a tsunamiNever go to the shore to watch a tsunami

4.4. An unexpected rise or fall of sea level may indicate An unexpected rise or fall of sea level may indicate an impending tsunamian impending tsunami