Seafloor Features


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Seafloor Features

  1. 1. Oceanography
  2. 2. • Ocean: >3 million sq km – Pacific, Atlantic, Indian, Arctic – all are actually connected • Sea:<3 million sq km, partly enclosed by land
  3. 3. Measuring Ocean Depth: • First done with knotted ropes • later, sonar (SOund NAvigation Ranging) used sound waves • most ocean mapping now done with satellites
  4. 4. Sonar Sonar
  5. 5. Sound Density Image
  6. 6. Marine Geology • Many seafloor features are caused by plate tectonics; others by erosion and deposition • 2 sections of seafloor – 1. ocean basin: deep; oceanic crust
  7. 7. • 2. continental margins: shallow; cont. crust covered by water –active margins: have a trench or MOR –passive margins: none
  8. 8. Passive Margin
  9. 9. Passive Margin
  10. 10. Passive Margin (Atlantic-Type Margin) • continental margin moving away from the mid-ocean spreading center; • these margins have no mountain building activities; • get thick sediment deposits here that cover up the oceanic crust and the boundary between oceanic and continental crust
  11. 11. Passive Margin (Atlantic-Type Margin)
  12. 12. Active Margin (Pacific-Type Margin) • • • • • • continental margin is moving toward a subduction zone; is marked by active volcanoes, many earthquakes, and young mountains and elevation of land (because overlying plate is pushed up by subducting plate) oceanic crust and overlying sediment are partially melted at an active margin as plate is pulled downward; continents can grow here as ocean-bottom structures melt and weld onto the continental plate and as volcanoes erupt and spew lava area of intense earthquakes because friction builds up when upper plate scraps across subducting plate (like a up-down transform fault); strain on the rocks build up and eventually the rocks fail (get a fault zone) where subducting plate is old, cold and dense, it sinks into the mantle as a steeply dipping slab (occurs in western Pacific) -- can get volcanic activity here that will create new, small spreading centers (back-arc spreading centers); continental plate will retreat from these small spreading centers (low stress convergence) where subducting plate is young, warm and buoyant, slab dips at a gentle angle, resulting in volcanic activity that erupts on land; continental plate will advance here (high stress convergence)
  13. 13. Active Margin
  14. 14. Active Margin
  15. 15. Active Margin
  16. 16. Continental Margins • 1.Continental shelf: shallow; flat; continental crust covered by H20. –active margin: shelf is narrow; bordered by ocean trench and coastal mountains –passive margin: wide, flat shelf; no trench, flat coastal land
  17. 17. Active Margins These are Profiles of the Ocean Floor
  18. 18. Passive Margins These are Profiles of the Ocean Floor
  19. 19. • 2. Continental slope: steep boundary between oceanic (thin) and continental (thick) crust – active margin: slope ends at trench
  20. 20. • 3. Continental rise: gently sloping, thick pile of sediments at base of continental slope – passive margins only
  21. 21. • Submarine Canyon: deep cut at right angle to shelf – may be a drowned river valley – may be formed by fast-moving currents that create landslides that erode the canyon
  22. 22. Submarine Canyon
  23. 23. B. Ocean Basin • 5. Abyssal plains: flat, thick layers of sediments. • 6. Abyssal hills: small hills; probably parts of crust not yet covered by sediments.
  24. 24. • 7. Seamounts: underwater volcanoes
  25. 25. 8. Guyot: seamount w/flat top that was eroded by waves
  26. 26. 9. Mid-ocean ridge(MOR): undersea chain of volcanic mountains; where new crust is formed.
  27. 27. • MOR’s have active hydrothermal vents or “black smokers” where mineral-rich, superheated water comes out • site of chemosynthetic ecosystems where life is not based on sunlight but on the chemicals in the water
  28. 28. Black Smoker Tube worms
  29. 29. Birth of Deep Sea Vents (click on picture)
  30. 30. • Trench: long, narrow, deep; parallel to coast –converging boundary –ocean crust destroyed –deepest is Marianas Trench, 11km below sea level
  31. 31. Trench
  32. 32. Side View of Ocean Floor Features
  33. 33. Click on the picture below to get Interactive: Follow the instructions on the screen
  34. 34. References • tent/investigations/es2301/es2301page05.cfm