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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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bathymetry the study of ocean floor contours
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

continental margins ocean basins

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

continental margins
Continental Margins

Passive margins

Active margins


passive margin

active margin

continental margins13
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.

continental shelves are seaward extensions of the continents
Continental Shelves Are Seaward Extensions of the Continents
  • The features of a passive continental margin:
  • Vertical exaggeration 50:1
  • (b) No vertical exaggeration
  • margin.
submarine canyons form at the junction between continental shelf continental slope
Submarine Canyons Form at the Junction between Continental Shelf & Continental Slope

turbidity currents

how do canyons form
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

topology of deep ocean basins differs from that of the continental margin
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.

hydrothermal vents
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

deep ocean basins
Deep-Ocean Basins

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

volcanic seamounts guyots project above the seabed
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.

deep ocean basins26
Deep-Ocean Basins

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

deep ocean basins27
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.

the abyss
The Abyss

abyssal plains: flat, featureless expanses of seafloor

covered w/ sediment

between continental margins & oceanic ridges

3700-5500 m

why so flat?