Geology lecture 17

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Geology lecture 17

  1. 1. O ceans and Coasts Chapter 18
  2. 2. Outline• Ocean exploration & oceanography• The globes’ oceans -Lithosphere density and ocean basins -Global ocean landscape• Submarine landscape -Major zones (shelf to Abyssal plains) – reflection of tectonics -Continental margins, submarine canyons -Ocean water composition, temperature• Ocean dynamics -Currents, Coriolis effect, tides, waves• Coastal landforms -beaches, barrier islands, rocky coasts, tidal flats, reefs etc.. Chapter 18 Chapter 18
  3. 3. Oceans• Humans have explored the ocean for centuries.• Before 1800s, sea floors was unknown • HMS Challenger (1872-1876) 1st oceanography study • Dredged sea floor rocks • Measured seawater, depth, currents • Analyzed water • Collected biota Chapter 18
  4. 4. Oceans• Our knowledge of oceans has expanded greatly: • Oceanography – study of ocean water and its movement • Marine geology – study of ocean floor rocks/seds • Marine biology – study of ocean life Chapter 18
  5. 5. Oceanography• Instruments have greatly expanded our knowledge. • Submarine exploration – Alvin (WHOI) • Bathymetric mapping – sonar/radar • Ocean drilling- recovers time archived below the seafloor • Major drilling projects (DSDP, ODP, IODP) Chapter 18
  6. 6. Oceanography• Seismic reflection profiling. • Sound waves pass through water and sediment • Some waves bounce off each subsurface layer • Travel time of reflected waves captured by geophones • Used to make images of ocean floor geology Chapter 18
  7. 7. Outline• Ocean exploration & oceanography• The globes’ oceans -Lithosphere density and ocean basins -Global ocean landscape• Submarine landscape -Major zones (shelf to Abyssal plains) – reflection of tectonics -Continental margins, submarine canyons -Ocean water composition, temperature• Ocean dynamics -Currents, Coriolis effect, tides, waves• Coastal landforms -beaches, barrier islands, rocky coasts, tidal flats, reefs etc.. Chapter 18 Chapter 18
  8. 8. The Global Oceans• Ocean covers 70.8% of Earth’s surface • Largest reservoir in hydrologic cycle• Oceans… • Serve as basis for life • Regulate climate • Cycle mass and energy • Linked to atmosphere, • lithosphere, biosphere Chapter 18
  9. 9. Global Landscape• Oceans exist because of lithosphere differences. • Continental lithosphere • Oceanic lithosphere• Ocean basins collect Chapter 18
  10. 10. Global Ocean Landscape• The world ocean is • Tectonic processes• Biotic activity: Chapter 18
  11. 11. Global Ocean Landscape• Present configuration of tectonic plates… • Most continental crust in • Most oceanic crust in Chapter 18
  12. 12. Outline• Ocean exploration & oceanography• The globes’ oceans -Lithosphere density and ocean basins -Global ocean landscape• Submarine landscape -Major zones (shelf to Abyssal plains) – reflection of tectonics -Continental margins, submarine canyons -Ocean water composition, temperature• Ocean dynamics -Currents, Coriolis effect, tides, waves• Coastal landforms -beaches, barrier islands, rocky coasts, tidal flats, reefs etc.. Chapter 18 Chapter 18
  13. 13. Undersea Landscapes• Sea floor bathymetry • Continental shelf – • Continental slope – • Abyssal plain – Chapter 18
  14. 14. Undersea Landscapes• Sea floor reflects • Continental shelf – • Continental slope – • Abyssal plain – Chapter 18
  15. 15. Undersea LandscapesContinental margins:• Passive• Active western SA: activeEastern NA: passive Chapter 18
  16. 16. Undersea Landscapes• Submarine canyons • Associated with • Carved during • Funnel sediments to • Submarine fans grow where Chapter 18
  17. 17. Ocean Water Composition• Normal marine salinity, reflecting dissolved ions, is • Dissolved ions derive from • Ions mostly Chapter 18
  18. 18. Ocean Water Composition• Surface salinity can vary. • Higher salinity  • Lower salinity • Salinity becomes Chapter 18
  19. 19. Ocean Water Temperature• Ocean surface T varies• Water buffers• Water T approaches• Ocean bottom water is Chapter 18
  20. 20. Outline• Ocean exploration & oceanography• The globes’ oceans -Lithosphere density and ocean basins -Global ocean landscape• Submarine landscape -Major zones (shelf to Abyssal plains) – reflection of tectonics -Continental margins, submarine canyons -Ocean water composition, temperature• Ocean dynamics -Currents, Coriolis effect, tides, waves• Coastal landforms -beaches, barrier islands, rocky coasts, tidal flats, reefs etc.. Chapter 18 Chapter 18
  21. 21. Oceanic Currents• Currents continuously • Surface currents (upper 100 m) - due to • Current motion creates Chapter 18
  22. 22. The Coriolis Effect• Earth rotation deflects• Acts as an• Coriolis deflection sense depends upon…• Merry-go-round analogy: Chapter 18
  23. 23. The Coriolis Effect• Surface winds & currents are • North hemisphere: • S-moving winds/currents deflected • N-moving winds/currents deflected • South hemisphere. • N-moving winds/currents deflected • S-moving winds/currents deflected Chapter 18
  24. 24. Vertical Oceanic Currents• Currents also transport • Downwelling – • Upwelling –• Wind perpendicular to shore • Onshore – • Offshore – Downwelling Upwelling Chapter 18
  25. 25. Vertical Oceanic Currents• Thermohaline contrast also • Temp – cold water • Salinity – More saline water• Polar water is both• Deep ocean waters are Chapter 18
  26. 26. Oceanic Currents• Sinking polar water is • This process carries • These surface currents• System forms a Chapter 18
  27. 27. Tides• Sea level rises and falls • High tide – • Low tide – • Tidal reach – • Intertidal zone Chapter 18
  28. 28. Tides• Caused by: • Gravitational pull of • Centrifugal forces from• Orbiting moon creates strongest tidal effects. • Sublunar bulge follows • Smaller bulge occurs • Bulges = ; low tides = Chapter 18
  29. 29. Tides• Lunar & solar tidal effects • Positive alignment yields • Negative alignment results in Chapter 18
  30. 30. Waves• Ocean waves develop via friction from wind on water. • Gentle wind  ; gales • Waves move upper part• Wave height, length, and period depend on Chapter 18
  31. 31. Waves• Wave anatomy: • Crest – • Trough – • Wavelength –• Depth of influence (wave base) is ½ the wavelength. • Above wave base, water • Below wave base, water Chapter 18
  32. 32. Waves• As waves approach shore, • Friction • Near surface, waves • Wave• This zone features Chapter 18
  33. 33. Waves• Waves that crash onto beach • Wave energy dissipated by • Creates • Water surge (swash) • Gravity pulls Chapter 18
  34. 34. Wave Refraction• Irregular shoreline • As waves drag on bottom,• This process, wave refraction, has consequences: • Wave attack concentrated • Wave attack is dissipated • Tend to Chapter 18
  35. 35. Longshore Currents• Sediment is transported along shore. • Oblique waves push • Gravity then pulls • Zig-zag pattern Chapter 18
  36. 36. Rip Currents• Develop when wave flow is • Water piles up on beach, • Rip current develops • Rip currents are • Rip currents dissipate away from Chapter 18
  37. 37. Outline• Ocean exploration & oceanography• The globes’ oceans -Lithosphere density and ocean basins -Global ocean landscape• Submarine landscape -Major zones (shelf to Abyssal plains) – reflection of tectonics -Continental margins, submarine canyons -Ocean water composition, temperature• Ocean dynamics -Currents, Coriolis effect, tides, waves• Coastal landforms -beaches, barrier islands, rocky coasts, tidal flats, reefs etc.. Chapter 18 Chapter 18
  38. 38. Coastal Landforms• A variety of landforms Chapter 18
  39. 39. Beaches• Dominated by• Gravel beaches reflect• Muds • Turbulent surf • Muds transported to Chapter 18
  40. 40. Beaches• Beach sediment composition reflects • Quartz • Carbonates • Resistant Chapter 18
  41. 41. Beaches• Beaches develop distinctive• Profiles change • Summer – • Winter – Chapter 18
  42. 42. Beaches• Distinct zones exist along a beach profile. • Foreshore or intertidal – • Beach face – • Backshore – • Beyond reach of • Often exhibit Chapter 18
  43. 43. Beaches• Longshore currents move • This process, beach • Beach drift builds Chapter 18
  44. 44. Beach Drift Beach DriftThis animation illustrates the sawtooth motion that causessand to gradually migrate along beaches in a process calledbeach drift, and shows how this can create sand spits inplaces where the coastline indents landward. For moreinformation, see Section 18.6 Where Land Meets Sea:Coastal Landforms starting on p. 638 and Figure 18.20 inyour textbook. Chapter 18
  45. 45. Barrier Islands• Barrier islands are • Form where • Protected backwater area called • Common places for • They are Chapter 18
  46. 46. Tidal Flats• Form in intertidal zones • Common behind • Thinly laminated • Ancient tidal flat sediments Chapter 18
  47. 47. Rocky Coasts• Bedrock intersects • Wave action is • Wave energy acts • Develop unique Chapter 18
  48. 48. Rocky Coasts• Wave-cut notches – • Cliff • Over time, cliff • An erosional remnant of • Often exposed at Chapter 18
  49. 49. Rocky Coasts• Rocky headlands are • Refracted waves focus • Erosion from both sides • Collapse of the Chapter 18
  50. 50. Wetlands• Wetlands cover • Develop in places protected from • Fuel high • Vegetation governed by • Temperate - • Tropical – Chapter 18
  51. 51. Estuaries• River valleys flooded by • Mixed • Modern estuaries are • Rivers carved canyons during • Sea-level rise Chapter 18
  52. 52. Fjords• Flooded • Form spectacular • Notable examples found in… • Norway. • British Columbia. • New Zealand. Chapter 18
  53. 53. Reefs• Coral reefs grow in • Large structures of • Most biologically productive Chapter 18
  54. 54. Reefs• Coral reefs • Reefs alter • Protect • Abundant debris is shed to adjacent environments. Chapter 18
  55. 55. Reefs• Coral atolls  reefs formed on • Reef is established when • After extinction, • Reef can easily keep pace • Reef continues long after Chapter 18
  56. 56. Coastal Variability• Plate tectonic setting governs • Passive margin – • Active margin – Chapter 18
  57. 57. Coastal Variability• Global sea-level changes effect • Inflation/deflation of • Glaciation/deglaciation • Pleistocene glaciations Chapter 18
  58. 58. Coastal Variability• Emergent coasts experience relative sea-level • Via uplift due to • Via sea-level• Emergent coasts characterized by… • River • Terraces representing Chapter 18
  59. 59. Coastal Variability• Submergent coasts experience relative sea-level • Subsidence of • Global sea-level• Submergent coasts characterized by Chapter 18
  60. 60. Coastal Variability• Shoreline character is linked to • Balance between • Accretionary coasts – • Erosional coasts – Chapter 18
  61. 61. Coastal Variability• Climate is a strong influence on • Harsh weather enhances • Calm weather favors • Tropics – • Temperate – • Arctic – Chapter 18
  62. 62. Coastal Problems• Sea-level change. • Sea level is • Rate of • People living in Chapter 18
  63. 63. Coastal Problems• Beach • Storms (e.g. hurricanes) • Human development in coastal settings • Construction in coastal settings is Chapter 18
  64. 64. Mitigating Coastal Problems• Artificial barriers built to • Groins, jetties, breakwaters • Usually produces • Deposition is enhanced • BUT, erosion is accelerated Chapter 18
  65. 65. Mitigating Coastal Problems• Approach to combat erosion • Seawalls may hasten erosion. • Wave energy is • Erosion enhanced • Seawalls can Chapter 18

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