Creation, Aging and Recycling of the Ocean Floor - PowerPoint PPT Presentation

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Creation, Aging and Recycling of the Ocean Floor

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  1. Creation, Aging and Recycling of the Ocean Floor How is the ocean floor made? Why does the ocean floor get deeper with age? How are volcanic arcs made and why are they so dangerous?

  2. Formation of Ocean Lithosphere

  3. Formation of Ocean Lithosphere Mid-ocean ridges-- global circuit of plate divergence-- youngest ocean floor-- shallowest ocean floor Architecture of oceanic plates-- seismic profiling-- ocean drilling-- fossil slivers of ocean floor

  4. Seismic Profiling (sound energy)

  5. Ocean Drilling • International program(20 nations; began 1968) • 2-month cruises • Deepest hole: 2 kmBut, new vessel will drillto >6km!

  6. Fast vs. Slow Spreading Fast Spreading Ridge (10-20 cm/yr) Slow Spreading Ridge (1-5 cm/yr)

  7. Mid-Ocean Ridges Uniform process of mantle melting, lava freezing- magma chambers- effects of spreading rate- segmentation

  8. Ocean Crust Layering

  9. Superfast Spread Crust Mission to Hole 1256D

  10. Superfast Spread Crust Mission to Hole 1256D

  11. o 10 cm Mineralized Volcanic Breccia (1027-1029 mbsf) o

  12. Sea floor deepens with distance from the spreading ridges -- why?

  13. Plate Aging involves heat loss through Conductive Cooling Relation: Depth increases with the square root of age

  14. A New View on Plate Cooling Adam & Vidal, Science, April 2, 2010

  15. And, heat loss through Hydrothermal Circulation

  16. Hydrothermal Circulation

  17. Hydrothermal Circulation • Natural consequence of porous, hot rock and seawater • Chemical exchange • Fluid venting -- black smokers • Chemosynthetic ecosystems • Crack sealing and sedimentation

  18. Hydrothermal Vent Sites

  19. Hydrothermal Vents Video

  20. The ocean floor ages and accumulates sediments

  21. Plate Aging and Recycling Slab sinking -- denser than asthenosphere

  22. Plate Subduction and Melting

  23. Pacific NW

  24. Mt St Helens Water, from slab, promotes mantle melting and leads to explosive danger of arc volcanoes

  25. Krakatoa (1883)Tambora (1815)

  26. Toba (71,000 B.C.) • 3000 times as big as Mt St Helens • - Sulfuric acid and dust blocked sunlight, reducing temperatures 5°C for several years • - May have reduced human population to <5000!

  27. Mt Hood

  28. Broken Top

  29. Three Sisters

  30. Crater Lake (Mt. Mazama)

  31. Volcanic ash (tephra)