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Exploring Bathymetry: The Ocean Floor's Secrets Unveiled

Chapter 4 of "Under the Sea" delves into bathymetry—the study of ocean floor topography. It covers the history of ocean mapping techniques, from using ropes to modern advancements like echo sounding, multi-beam systems, and satellite altimetry. Learn about the features of continental margins, the significance of oceanic ridges, and the role of submarine canyons. Discover how innovations have improved our understanding of underwater landscapes, from the deep-sea trenches to the formation of seamounts and guyots, revealing the complex interplay of Earth's geological processes beneath the waves.

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Exploring Bathymetry: The Ocean Floor's Secrets Unveiled

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  1. Under the Sea Chapter 4

  2. Bathymetry • Discovery & study of the ocean floor • History: • throw heavy rope tied to a rock over the side of the boat • measured fathoms as arm lengths • Improvements: • Echo Sounding, Multi-beam Systems & Satellite Systems

  3. Echo Soundings • After Titanic (1912) & WWI increase in bathymetry. Why? • Looked for better way to study ocean • Developed a sound pulse and listen for echo • Similar to dolphins, porpoises, & ocras which use echolocation

  4. Echo Sounding Problems • ship position not certain • speed of sound varies with temp, pressure, salinity and affects readings • images were fuzzy

  5. Multi-beam Systems • 121 beams from ship to take echo sounding • more accurate reading • Like “mowing the lawn” gave a section to interpret rather than a single point

  6. Satellite Altimetry • Satellites measure small variations in the elevation of surface water • Many radar pulses each second • Used sophisticated calculations to determine the sea floor

  7. Topography of Ocean Floors • Seabed topography is due to isostatic equilibrium • Balancing of less dense continental plate and more dense oceanic plate over mantle • Submerged outer edge of continent = continental margin • Deep sea floor = ocean basin

  8. Continental Margins • Active Margins: • continental margins of converging plates • Lots of volcanic & earthquake activity • Ex: Pacific Plate • Passive Margins: • continental margins of diverging plates • Little volcanic & earthquake activity • Ex: Mid-Atlantic Ridge

  9. 3 types of Continental Margins • Continental Shelf • Continental Slope • Continental Rise

  10. Continental Shelf • Shallow submerged extension of continent • Features: hills, depressions, sedimentary rocks, & mineral/oil deposits • Gentle incline • Consists of material from erosion (ex: river mouths) which can determine the width of shelf • Affected by sea level: ice age can change isostatic equilibrium • Used for resources: minerals & oil

  11. Continental Slope • Transition between the continental shelf & the ocean floor • Sediments from shelf are transported over the side creating a slope • Often scraped off by subduction • Shelf break = abrupt transition from continental shelf to the continental slope

  12. Submarine Canyons • Canyons cut into shelf & slope • Fan-shaped • Usually right angle to shoreline • Formed from erosion and/or earthquakes • Earthquakes create turbidity currents (avalanche of sediment)

  13. Continental Rise • Sediment at base of slope transported from shelf • Deep-ocean currents &/ turbidity currents

  14. Deep-Ocean Basins • Oceanic ridge systems and adjacent sediment-covered plains • Includes: • Oceanic Ridges • Hydrothermal Vents • Abyssal Plains & Abyssal Hills • Seamounts & Guyots • Trenches & Island Arcs

  15. Oceanic Ridges • Mountainous chain of basaltic rock at center of spreading center • Formed from divergent boundaries • Old rocks far away from center • Young rocks at center • Not in straight line, broken up by transform faults and fracture zones (remnants of transform faults)

  16. Hydrothermal Vents • Hot springs from ridge floor • Forms from water into cracks of ridge floor and venting out • Water is hot, acidic, filled with minerals, and gases • Unusual organisms live here

  17. Abyssal Plains & Abyssal Plains • Plains: • flat sediment covered floor found on periphery of all oceans • Sediment from turbidity currents or winds • Hills: • small volcanoes, from diverent boundaries, parallel / borders ridges

  18. Seamounts & Guyots • Formed from old hotspots • Seamounts: • old volcanoes never breeched surface • Guyot: • former islands eroded down • Ex: 100+ small islands of Hawaii

  19. Trenches & Island Arcs • Trenches: • Deep depression in ocean floor • Deepest part of ocean • Forms from subduction zones • Island Arcs: • chain of volcanic islands from subduction zones • Ex: Aleutian Islands

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