GEOG 100--Lecture 17--Oceans

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GEOG 100--Lecture 17--Oceans

  1. 1. Coastal Geomorphology:Coastal Geomorphology:The Oceans, CoastalThe Oceans, CoastalProcesses, and LandformsProcesses, and LandformsThe Oceans, CoastalThe Oceans, CoastalProcesses, and LandformsProcesses, and LandformsChapter 12Chapter 12
  2. 2. The Movements of The OceansThe Movements of The Oceans• CurrentsCurrents• TidesTides• Wave motionWave motion
  3. 3. Warm and Cold Ocean CurrentsWarm and Cold Ocean Currents
  4. 4. Ocean Water:Ocean Water:Temperature, Salinity and DensityTemperature, Salinity and Density• TemperatureTemperature–Latitude, depth, and locationLatitude, depth, and location• SalinitySalinity– Dissolved mineral salts (sodium chloride, magnesium,Dissolved mineral salts (sodium chloride, magnesium,sulfur, calcium, potassium, etc.)sulfur, calcium, potassium, etc.)– Related to evaporation rates and fresh water inflowRelated to evaporation rates and fresh water inflow• DensityDensity– Related to temperature, salinity and depthRelated to temperature, salinity and depthThese three variables set up conditions for a globalThese three variables set up conditions for a globalthermohaline circulationthermohaline circulation
  5. 5. Currents: Thermohaline CirculationCurrents: Thermohaline Circulation
  6. 6. Currents: SurfaceCurrents: SurfaceDriven by temperature differences, wind, coriolis forceDriven by temperature differences, wind, coriolis forceDriven by temperature differences, wind, coriolis forceDriven by temperature differences, wind, coriolis force
  7. 7. TidesTides• A “bulge” in the world’sA “bulge” in the world’soceans, caused by theoceans, caused by thegravitational pull of thegravitational pull of themoon and sunmoon and sunFFgg == G mG m11 mm22dd22
  8. 8. TidesTides• Tidal range—the differenceTidal range—the differencebetween high and low tidebetween high and low tide• Affected by the shape of theAffected by the shape of thecoastline and seafloorcoastline and seafloor• Spring tides—highest tides,Spring tides—highest tides,strong and quickstrong and quick– Occur when sun, moon, and EarthOccur when sun, moon, and Earthline up (the sea “springs” up andline up (the sea “springs” up andback)back)• Neap tides—lowest tidesNeap tides—lowest tides– Sun and moon at right angles withSun and moon at right angles withrespect to Earthrespect to Earth– Neap = A low incline of bend (whenNeap = A low incline of bend (whengraphed)graphed)
  9. 9. Monthly Tidal CycleMonthly Tidal Cycle
  10. 10. Extreme High TidesExtreme High Tides• The Bay of Fundy• A 50’ (15m) tidal fluctuationis common (x2)•A tidal bore (several in. toseveral ft. high) rushes milesup the Petitcodiac River inNew Bruswick
  11. 11. Landforms shaped by extreme tidesLandforms shaped by extreme tides
  12. 12. 1212Extreme tides: Mont Saint Michel, FranceExtreme tides: Mont Saint Michel, France1212Low tide High tide
  13. 13. Waves and Wave DynamicsWaves and Wave Dynamics
  14. 14. Waves and Wave DynamicsWaves and Wave Dynamics• Period—The time it takes two successivePeriod—The time it takes two successivewaves (from crest to crest, or from trough towaves (from crest to crest, or from trough totrough) to pass a given pointtrough) to pass a given point• Fetch—The distance over which the windFetch—The distance over which the windblows, creating wavesblows, creating waves
  15. 15. Waves and Wave DynamicsWaves and Wave Dynamics• Factors affecting open ocean waves:Factors affecting open ocean waves:–FetchFetch•The greater the distance over which the wind blows,The greater the distance over which the wind blows,the larger the wavesthe larger the waves–Wind strengthWind strength•The stronger the wind, the larger the wavesThe stronger the wind, the larger the waves–Wind durationWind duration•The longer the wind blows, the more waves will beThe longer the wind blows, the more waves will becreatedcreated
  16. 16. Wave BaseWave BaseWave base
  17. 17. Waves of Oscillation vs. TranslationWaves of Oscillation vs. TranslationWaves of oscillationWaves of translation
  18. 18. Waves of Oscillation (Transition)Waves of Oscillation (Transition)andandWaves of TranslationWaves of Translation• Water molecules on the open ocean move in aWater molecules on the open ocean move in acircular motioncircular motion– The motion passes through the water, but the waterThe motion passes through the water, but the waterdoesn’t move forward (to oscillate is to move up anddoesn’t move forward (to oscillate is to move up anddown)down)– What moves the water forward is wind blowing over theWhat moves the water forward is wind blowing over thesurface and the movement of currentssurface and the movement of currents• Water molecules that reach the shore have theirWater molecules that reach the shore have theircircular motion interruptedcircular motion interrupted– Their energy is translated into the shore face (it passesTheir energy is translated into the shore face (it passesfrom the water to the land, where it does work to movefrom the water to the land, where it does work to movematerial—like sand—around)material—like sand—around)
  19. 19. Wave BreakWave Break
  20. 20. Wave Refraction,Wave Refraction,Longshore Current and Beach DriftLongshore Current and Beach Drift
  21. 21. Wave Refraction andWave Refraction andLongshore CurrentLongshore Current• As waves reach the shore and “feel” the bottom,As waves reach the shore and “feel” the bottom,they slow and breakthey slow and break• The direction of wave break follows the underwaterThe direction of wave break follows the underwatertopographytopography• This causes the wave to “bend” and become moreThis causes the wave to “bend” and become moreparallel to the shorelineparallel to the shoreline– This bending is calledThis bending is called wave refractionwave refraction• As it breaks from one side to the other, it creates aAs it breaks from one side to the other, it creates acurrentcurrent– This current, called theThis current, called the longshore currentlongshore current picks up andpicks up andmoves sediment (sand) down the shoremoves sediment (sand) down the shore
  22. 22. Erosional EnvironmentsErosional Environments• If there is not enough sediment replacing what’sIf there is not enough sediment replacing what’sbeing lost through wave erosion/longshore current,being lost through wave erosion/longshore current,erosion will occur, creating a rocky coastlineerosion will occur, creating a rocky coastline– Dam or channelized streams and sediment can’t get toDam or channelized streams and sediment can’t get tothe beachthe beach• Erosive environments create distinctive landformsErosive environments create distinctive landforms– rocky headlands and pocket beaches, sea arches androcky headlands and pocket beaches, sea arches andsea stacks, wave-cut cliffs, wave-cut platforms, wave-sea stacks, wave-cut cliffs, wave-cut platforms, wave-built terraces, etc.built terraces, etc.
  23. 23. Wave Energy is Concentrated atWave Energy is Concentrated atHeadlands and Dissipated in BaysHeadlands and Dissipated in Bays
  24. 24. Wave Motion and WaveWave Motion and WaveRefractionRefraction
  25. 25. Wave Energy is Concentrated atWave Energy is Concentrated atHeadlands and Dissipated in BaysHeadlands and Dissipated in Bays
  26. 26. Laguna Beach, CALaguna Beach, CAHeadlandsHeadlands
  27. 27. Headland ErosionHeadland Erosionand the Formation of Sea Archesand the Formation of Sea Arches
  28. 28. Stacks and CliffsStacks and CliffsVictoria, AustraliaVictoria, Australia
  29. 29. Depositional Environments:Depositional Environments:The Structure of a BeachThe Structure of a BeachThe Structure of a BeachThe Structure of a Beach
  30. 30. Barrier Island StructureBarrier Island Structure
  31. 31. 3131Barrier Island CoastBarrier Island CoastPadre Island, TexasPadre Island, Texas
  32. 32. Common Depositional LandformsCommon Depositional Landforms
  33. 33. Lagoons, Marshlands, and theLagoons, Marshlands, and theFormation of New CoastlinesFormation of New Coastlines
  34. 34. Submergent CoastlinesSubmergent Coastlines(Prepare to see more of these!)(Prepare to see more of these!)(Prepare to see more of these!)(Prepare to see more of these!)Ria CoastFjord Coast
  35. 35. Emergent CoastlinesEmergent Coastlines(Common in tectonically active areas)(Common in tectonically active areas)(Common in tectonically active areas)(Common in tectonically active areas)
  36. 36. Formation of a Wave-cut PlatformFormation of a Wave-cut Platformand Uplifted Marine Terracesand Uplifted Marine Terraces
  37. 37. ““Any serious researcher would be hard-Any serious researcher would be hard-pressed to find a marina, a sea wall, or anypressed to find a marina, a sea wall, or anyother human structure along the shoreline thatother human structure along the shoreline thatdoes not pose some long-term deleteriousdoes not pose some long-term deleteriouseffects to both the natural and culturaleffects to both the natural and culturalenvironments it attempts to protect.”environments it attempts to protect.”----Physical Geography: Earth’s Interconnected SystemsPhysical Geography: Earth’s Interconnected SystemsAngela Orr, 2007Angela Orr, 2007Coastal Stabilization andCoastal Stabilization andHuman ImpactHuman Impact
  38. 38. Coastal Stabilization StructuresCoastal Stabilization Structures
  39. 39. 3939Coastal Stabilization and HumanCoastal Stabilization and HumanImpactImpact• Damming and channelizing streamsDamming and channelizing streams–Causes a loss of sediment where streams emptyCauses a loss of sediment where streams emptyinto the sea. Without sediment, the beach willinto the sea. Without sediment, the beach willerode away.erode away.• SeawallsSeawalls• Groynes (groins)Groynes (groins)• Breakwaters and jettiesBreakwaters and jetties
  40. 40. 4040Groynes (groins)Groynes (groins)
  41. 41. 4141• Can you tell which way the longshore current isCan you tell which way the longshore current ismoving material?moving material?• Once you put up one groyne, you need to keepOnce you put up one groyne, you need to keepbuilding them all along the shore to keep erosion frombuilding them all along the shore to keep erosion fromdestroying property downshore from your firstdestroying property downshore from your firststructure. Note the severe erosion at the top of thestructure. Note the severe erosion at the top of thephoto where the groynes stop.photo where the groynes stop.
  42. 42. BreakwaterBreakwater
  43. 43. 4343BreakwaterBreakwater• These breakwaters are creating tombolos inThese breakwaters are creating tombolos inthe wave shadow behind them.the wave shadow behind them.
  44. 44. The Example of Marina del Rey,The Example of Marina del Rey,CACA

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