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Continental Margins & Ocean Basins. Bathymetry: The Study of Ocean Floor Contours. Early bathymetric studies were often performed using a weighted line to measure the depth of the ocean floor. Advances in Bathymetry  Echo sounding  Multibeam Systems  Satellite Altimetry.

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Continental Margins & Ocean Basins

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Continental Margins & Ocean Basins


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Bathymetry:The Study of Ocean Floor Contours

Early bathymetric studies were often performed using a weighted line to measure the depth of the ocean floor.

Advances in Bathymetry

 Echo sounding

 Multibeam Systems

 Satellite Altimetry


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Ocean Floor Is Mapped by Bathymetry


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Bathymetry:The Study of Ocean Floor Contours


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Bathymetry:The Study of Ocean Floor Contours


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Bathymetry:The Study of Ocean Floor Contours


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Sea Floor Bathymetry as Measured by Satellite


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The Topography of Ocean Floors


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Ocean-Floor Topography Varies with Location


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Continental Margins & Ocean Basins

Continental Margins & Ocean Basins

What are the two classifications of ocean floor?

Continental Margins – the submerged outer edge of a continent

Ocean Basin – the deep seafloor beyond the continental margin


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Continental Margins

Passive margins

Active margins


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passive margin

active margin


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Continental Margins

shallow, submerged edge of the continent.

abrupt transition from continental shelf to the continental slope.

transition between the continental shelf & the deep-ocean floor.

accumulated sediment found at the base of the continental slope.


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Continental Shelves Are Seaward Extensions of the Continents

  • The features of a passive continental margin:

  • Vertical exaggeration 50:1

  • (b) No vertical exaggeration

  • margin.


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Continental Shelves Are Seaward Extensions of the Continents


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Cretaceous Period


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Continental Margins – Submarine Canyons


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California’s canyons


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Submarine Canyons Form at the Junction between Continental Shelf & Continental Slope

turbidity currents


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How do canyons form?

river erosion during previous glaciation periods

turbidity currents: rapid movement of a mass of sediment down a slope

~ avalanche

often caused by earthquakes


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Topology of Deep-Ocean Basins Differs from That of the Continental Margin

An oceanic ridge is a mountainous chain of young, basaltic rock at an active spreading center of an ocean.


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Mid-Atlantic Ridge


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Hydrothermal Vents

hydrothermal vents: spring of hot, mineral- and gas-rich seawater

near seafloor spreading centers

- 1977, Robert Ballard & J. Grassle in Alvin, at 3000 m

near the Galápagos Islands


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Deep-Ocean Basins

Hydrothermal vents are sites where superheated water containing dissolved minerals & gases escapes through fissures, or vents.


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Volcanic Seamounts & Guyots Project Above the Seabed

Seamounts are volcanic projections from the ocean floor that do not rise above sea level. Flat-topped seamounts eroded by wave action are called guyots.

Abyssal hills are flat areas of sediment-covered ocean floor found between the continental margins & oceanic ridges. Abyssal hills are small, extinct volcanoes or rock intrusions near the oceanic ridges.


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Deep-Ocean Basins

Trenches are depressions in the ocean floor caused by the subduction of a converging ocean plate.


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Deep-Ocean Basins

Island Arcs, chains of volcanic islands & seamounts, are usually found parallel to the edges of ocean trenches.

(left) As two oceanic plates converge, an island arc is formed by volcanic activity.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc.


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Trenches & Island Arcs Form in Subduction Zones


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The Abyss

abyssal plains: flat, featureless expanses of seafloor

covered w/ sediment

between continental margins & oceanic ridges

3700-5500 m

why so flat?


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