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The Oceans

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  1. The Oceans Steve Terrill/Stock Market

  2. Sandy Beach, North Carolina Barrier Island Fig. 17.1 Peter Kresan

  3. Boulder Beach, Massachusetts Fig. 17.2 Raymond Siever

  4. Wave height depends on: • Wind velocity • Wind duration • Distance over which wind blows

  5. Wave-generated Orbital Waves Fig. 17.3

  6. Wave characteristics • Length (L): distance between crests • Height (H) : vertical distance between crest and trough • Period (T): time for successive waves to pass a fixed point

  7. Velocity (V) of waves V = L/T

  8. Waves in shallow water • Wave height increases • Wave length decreases • Velocity decreases • Period doesn’t change

  9. Surf Zone Zone between where the waves break to point furthest up the shore where the waves wash up

  10. Changes in Waves as they Approach the Beach Fig. 17.4

  11. Wave refraction • Bending of wave crests as they approach the beach at a non-normal angle • Caused by the change in velocity of waves as a function of water depth

  12. Wave Refraction Fig. 17.6

  13. Waves Bending as they Approach the Beach Fig. 17.5 John S. Shelton

  14. Refraction at Headlands and Bays Fig. 17.7

  15. Longshore Drift Fig. 17.8

  16. Sediment transport near shore, parallel to the beach • Longshore drift: sediment carried by swash and backwash along the beach • Longshore currents: currents parallel to the beach within the surf zone

  17. Tides Twice daily rise and fall of the sea caused by the gravitational attraction between • Earth and moon (lunar tides) • Earth and sun (solar tides)

  18. Lunar Tidal Bulges Fig. 17.9

  19. Interaction between lunar and solar tides during the lunar month causes: • Neap tides: when two tidal components are out-of-phase, hence lower than usual, and • Spring tides: when two tidal components are in-phase, hence higher than usual.

  20. Earth-Moon-Sun Alignment and Neap-spring Tides Neap tides Spring tides Fig. 17.10

  21. Mont-Saint-Michel France Exposed tidal flats Fig. 17.11 Thierry Prat/Sygma

  22. Terrace Exposed at Low Tide Fig. 17.12 James Valentine

  23. Tidal Variations – Bay of Fundy High Tide Low Tide

  24. Tidal Variations – Kink Harbor, Alaska High Tide Low Tide

  25. Major parts of beaches • Offshore: from where the waves begin to feel bottom to the surf zone • Foreshore: includes the surf zone, tidal flats, and swash zone • Backshore: from beyond the swash zone to the highest level of the beach

  26. Major Parts of a Beach Fig. 17.13

  27. Sand budget The inputs and outputs of sediment by erosion and sedimentation.

  28. Sand Budget of a Beach Fig. 17.14

  29. Preventing beach erosion • Structural approaches (e.g., groins): typically cause increased erosion downcurrent of structure • Non-structural approaches (e.g., beach nourishment, land use planning): expensive, but don’t cause erosion in new areas

  30. Groin: Built to Prevent Updrift Erosion Causes Downdrift Erosion Erosion Deposition Phillip Plissin/Explorer

  31. Beach Nourishment, New Jersey U.S. Corps of Engineers, New York District

  32. Factors determining rates of erosion or deposition • Uplift • Subsidence • Rock type • Sea-level changes • Wave heights • Tidal range

  33. Sea Stacks Fig. 17.15 Kevin Schafer

  34. Wave-cut Terrace Exposed at Low Tide Fig. 17.16 John S. Shelton

  35. Southern Tip of Cape Cod Fig. 17.17 Steve Durwell/The Image Bank

  36. Past 160 Years of Shoreline Change, Southern Cape Cod Fig. 17.19

  37. Partially Developed Barrier Island Mainland Florida Lagoon BarrierIsland Gulf of Mexico Fig. 17.18 Richard A. Davis, Jr

  38. Uplifted Coastal Terrace Fig. 17.20 John S. Shelton

  39. Mapping the seafloor • Satellite measurements • Echo sounding profiles • Side-scan sonar • Manned and unmanned submersibles

  40. From Gravity Anomaly to Seafloor Topography D.T. Sandwell & W.H.F. Smith/Scripps Institute of Oceanography

  41. Congo Submarine Canyon Echo sounding profile Fig. 17.22

  42. Loiki SeamountImaged Using Side-scan Sonar Fig. 17.23 Ocean mapping Development center, University of Rhode Island

  43. The Benthic Explorer Unmanned Submersible Fig. 17.21 T. Kleindinst/Woods Hole Oceanographic Institute

  44. Topographic Profile of the North Atlantic Ocean Fig. 17.24

  45. Atlantic bathymetric features • Continental shelf • Continental slope • Continental rise • Abyssal plains • Seamounts • Mid-ocean ridge

  46. Pacific bathymetric features • Continental shelf • Continental slope • Trench • Abyssal plains • Seamounts • Mid-ocean rise

  47. Continentalshelf Continentalslope Continentalrise Fig. 17.25 Praxton & Haxby, 1996

  48. From the Continental Rise to the Mid-Atlantic Ridge Fig. 17.26

  49. Topography of the North Atlantic Ocean Fig. 17.27 Detail from H.C. Berannrket, based on Heezen & Tharp

  50. Topographic Profile of the Western Pacific Ocean Fig. 17.28