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TAMU OCNG 251 - Lecture 9a (Oceans)-(Waves)

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““We have to continually be jumping off cliffsWe have to continually be jumping off cliffsand developing our wings on the way downand developing our wings on the way down””Kurt VonnegutKurt VonnegutBeware of the man who works hard to learnBeware of the man who works hard to learnsomething, learns it, and finds himself nosomething, learns it, and finds himself nowiser than before. [wiser than before. [……] He is full of] He is full ofmurderous resentment of people who aremurderous resentment of people who areignorant without having come by theirignorant without having come by theirignorance the hard way.ignorance the hard way.Kurt Vonnegut, "Cat's Cradle"Kurt Vonnegut, "Cat's Cradle"OCNG 251: OceanographyOCNG 251: OceanographyTuesday,Tuesday, Nov. 18 Nov. 18, 2008, 2008The surface of the Ocean: 1) WavesThe surface of the Ocean: 1) Waves1.1.ReviewReview2.2.Waves:Waves:a.a.Anatomy of a waveAnatomy of a waveb.b.Wave motion: speed and energyWave motion: speed and energyc.c.Deep- & Shallow-water wavesDeep- & Shallow-water wavesReviewReviewa.a.IntroductionIntroduction!!Sediments are produced by the weathering (chemical andSediments are produced by the weathering (chemical andmechanical breaking down) of rocks into particles that are thenmechanical breaking down) of rocks into particles that are thenmoved by air, water, and ice.moved by air, water, and ice.!!Sediments can also be formed from the accumulation of shellsSediments can also be formed from the accumulation of shellsor micro- and macro-debris of organisms.or micro- and macro-debris of organisms.!!Sediments can therefore consist ofSediments can therefore consist of""Mineral particlesMineral particles""Fossil particlesFossil particlesb.b.Classification: Classification: Sediments can be subdivided on the basis of:Sediments can be subdivided on the basis of:!!The size of the particles (The size of the particles (grain sizegrain size))!!Their mode of formation (Their mode of formation (originorigin))!!Terrigenous sedimentsTerrigenous sediments!!Biogenous sedimentsBiogenous sediments!!Authigenic sedimentsAuthigenic sediments!!Volcanic sedimentsVolcanic sediments!!Cosmogenous sedimentsCosmogenous sedimentsReviewReviewc.c.Factors that control sedimentationFactors that control sedimentation!!Relationship between average grain size and energy of bottomRelationship between average grain size and energy of bottomcurrentscurrents!!Erosion, Transport and Deposition (sedimentation) depend onErosion, Transport and Deposition (sedimentation) depend onvelocity of current and grain sizevelocity of current and grain size!!Settling rate of suspended particles varies with diameterSettling rate of suspended particles varies with diameter(Stokes Law)(Stokes Law)d.d.Sedimentation in the OceansSedimentation in the OceansTwo major areas of sediment deposition on the basis of water depthTwo major areas of sediment deposition on the basis of water depthi.i.Shelf sedimentationShelf sedimentation: Shallow, close to terrigenous source: Shallow, close to terrigenous source(theoretical equilibrium)(theoretical equilibrium)ii.ii.Deep-Sea SedimentationDeep-Sea SedimentationTwo main sources:Two main sources:- External (terrigenous mud and sand)- External (terrigenous mud and sand)- Internal (biogenic particles, authigenic particles)- Internal (biogenic particles, authigenic particles)Three categories:Three categories:- Bulk emplacement- Bulk emplacement- Pelagic sediments- Pelagic sediments- Authigenic sediments- Authigenic sedimentsa.a.Anatomy of a waveAnatomy of a waveA wave can be regarded initially as an ideal a sinusoidal wave (thoughA wave can be regarded initially as an ideal a sinusoidal wave (thoughthe ideal regular waves bears little resemblance to real wavesthe ideal regular waves bears little resemblance to real wavesobserved at sea observed at sea ## irregular in form and period) irregular in form and period)Characteristics:• H: Height (2 x A)• L: Wavelength (from crest to crest)• T: Period (time required for two successive crests to pass a point)• h: Depth of water column below mean surface levelAAConcept of level: Geoid Concept of level: Geoid ## level surface on which the potentiallevel surface on which the potentialenergy is everywhere the sameenergy is everywhere the sameSea level change Sea level change ## Oscillation due to geological changes in the Oscillation due to geological changes in thehydrological cyclehydrological cycleSea levelSea levelAdapted from Pinet 2000Sea level change Sea level change ## Oscillation due to geological changes in the Oscillation due to geological changes in thehydrological cyclehydrological cycleAdapted from Garrison 2002Sea level changeSea level changea.a. Anatomy of a wave Anatomy of a waveIdeal wavesIdeal waves: If some water is lifted up and allowed to fall back: If some water is lifted up and allowed to fall backunder the action of gravity, its inertia will cause it to overshootunder the action of gravity, its inertia will cause it to overshootthe equilibrium position. Pressure forces will then push it backthe equilibrium position. Pressure forces will then push it backup and oscillation will ensue.up and oscillation will ensue.Energy can be transmitted at the interface (boundary) betweenEnergy can be transmitted at the interface (boundary) betweentwo fluids of different densities resulting in progressive two fluids of different densities resulting in progressive orbitalorbitalwaveswavesa.a.Anatomy of a waveAnatomy of a waveAll waves can be regarded asAll waves can be regarded as!!Progressive wavesProgressive waves, in that , in that energyenergy is travelling through, or across the is travelling through, or across thesurface of, the material (i.e. water)surface of, the material (i.e. water)!!Standing wavesStanding waves (i.e. plucked guitar strings) can be considered as the (i.e. plucked guitar strings) can be considered as thesum of two progressive waves of equal dimensions but traveling insum of two progressive waves of equal dimensions but traveling inopposite direction (lateropposite direction (later……))Waves can result from periodic and non-periodic disturbance of theWaves can result from periodic and non-periodic disturbance of thewater surface:water surface:In the case of non-periodic disturbances, the water particles areIn the case of non-periodic disturbances, the water particles aredisplaced from an equilibrium position displaced from an equilibrium position ##


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TAMU OCNG 251 - Lecture 9a (Oceans)-(Waves)

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