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Deep Ocean Topography. Mid-Ocean Ridges and Hydrothermal Vents Sarah Fawcett. Mid-Ocean Ridges. Linear mountain chains. Some of the largest features on Earth. 5km-2.6km deep. Roughly symmetrical in cross section. Thousands of kilometers wide.

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Deep ocean topography
Deep Ocean Topography

Mid-Ocean Ridges

and Hydrothermal Vents

Sarah Fawcett


Mid ocean ridges
Mid-Ocean Ridges

  • Linear mountain chains.

  • Some of the largest features on Earth.

  • 5km-2.6km deep.

  • Roughly symmetrical in cross section.

  • Thousands of kilometers wide.

  • Volcanoes, earthquakes, hills and mountains.


Location of ridges
Location of Ridges

  • Mid-Atlantic Ridge

    • 1855 - Fontaine Maury identified “shallow middle ground”.

    • 1950s - Heezen & Ewing proposed a continuous mountain range.

  • East Pacific Rise

    • Largest oceanic ridge.

    • 1870s - Challenger Expedition

    • 1950-60s - described by Heezen and Ewing.


Formation of ridges
Formation of Ridges

  • Divergent tectonic plate motions.

  • Tensional forces = thinning of oceanic crust and upwelling of magma, forming ridges.


Seafloor spreading

Lava buried by sediment as seafloor spreads away from ridge.

Spreading Rates:

Slow - 10mm/yr (Southwest Indian Ridge)

Fast - up to 160mm/yr (East Pacific Rise)

Correlation between global spreading rates and transgression of ocean waters onto the continents.

Early Cretaceous - Global spreading rates uniformly high

Marine sediments

Seafloor Spreading


Seafloor dating
Seafloor Dating

  • Paleomagnetic dating

    • Curie Point

    • Use spreading rate to calculate age of rock.

  • Age of the Seafloor

    • Gets older further from the ridge.


Hydrothermal vents
Hydrothermal Vents

  • Localized discharges of heated seawater.

  • Cold water percolates down into the crust through fissures.

  • Heated water rises and seeks a path to the surface.

  • Bursts into the ocean as hot as 400ºC but intense pressure from overlying ocean prevents it from boiling.

  • Accounts for amount of the Earth’s heat loss.


Growth of vents
Growth of Vents

  • Chimneys

    • Minerals leached from the crust - Zn, Fe, Cu.

    • Rapid growth rate.

  • “Black Smokers”

    • Hottest vents.

    • Iron monosulfide.

  • “White Smokers”

    • Cooler vents.

    • Compounds of Ba, Ca and Si.


Discovery of vents
Discovery of Vents

  • 1977 on East Pacific Rise

  • Near Galapagos Islands

  • ALVIN

    • Research submersible.

    • Wood’s Hole Oceanographic Institute.

    • Viewports, searchlights, mechanical arm, cameras.

    • First temperature measurement.



Life at hydrothermal vents
Life at Hydrothermal Vents

  • Harsh environment, yet abundant life:

    • Tubeworms

    • Crabs

    • Shrimp

    • Clams

    • Anemones

    • CHEMOSYNTHETIC BACTERIA

  • No photosynthesis

  • Bacteria convert sulfur to energy by chemosynthesis, forming base of foodchain.

  • Animals eat bacteria or bacteria live inside their bodies.

  • Origin of Life?



Baker cormier langmuir and zavala
Baker, Cormier, Langmuir and Zavala

  • Hydrothermal plumes along segments of contrasting magmatic influence, 15º20’ - 18º30N, East Pacific Rise: Influence of axial faulting. Geochemistry Geophysics Geosystems. Volume 2. September 2004. AGU and the Geochemical Society.

  • Theory: Greater incidence of hydrothermal vents on faster spreading ridge segments, not always the case - Tectonic forces can dominate.

    • Segment of ridge between Orozco and Rivera transform faults (15º18’N - 18º30’N).

    • 133 rock cores.

    • Comparison of hydrothermal environment of three adjacent but distinctly different segments.

    • Prediction:17ºN segment should have less extensive hydrothermal plumes than16º segments - slower spreading rate.

    • Opposite is true.


Deep ocean topography

  • 17ºN segment: plume incidence = mean of super fast spreading segments on the southern EPR.

  • Local permeability environment in the region controls amount of hydrothermal activity:

    • 16ºN segment: little indication of faulting, model for fast spreading rates, may have hydrothermal activity suppressed by volcanic flows that act as an impermeable cap over much of the segment.

  • Conclusion:

    • Tectonic forces can control the extent and nature of hydrothermal activity.

    • Documented for several sites on the Mid-Atlantic Ridge.

  • On a global scale, however this portion of the ridge follows the existing global correlation between plume incidence and spreading rate.