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Continental
Margin Morphology
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Overview
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| Overview |
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Three
types of margins exist along the borders of North America. The Atlantic
Ocean and the Gulf of Mexico margins are termed passive margins because
they are embedded within the North American Plate and simply ride along
with it as it moves. The western U.S. margin lies along the leading edge
of the North American Plate, where it bumps and grinds its way past oceanic
crust underlying the Pacific Ocean. This collision takes two forms. Through
most of the length of California, the U.S. margin is a strike-slip margin.
Here the North American Plate slips sideways past the Pacific Plate along
a system of near-vertical fractures in the earth collectively known as
the San Andreas Fault. Farther up the coast, the U.S. margin is a convergent
margin. In this region, the North American Plate is bulldozing its way
over a sliver of oceanic crust named the Juan de Fuca Plate.
The images
below have been generated using multibeam sonar data. These data provide
unprecedented views of the continental slope. Such undersea mapping is
providing fundamental knowledge about the geologic forces that shape the
ocean floor.
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| Example
Publications |
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Pratson,
L.F., and W.F. Haxby, 1997, Panoramas of the Seafloor: Scientific American,
v. 4, p. 82-87.
Pratson,
L.F., and W. Haxby, 1996, What is the slope of the U.S. continental slope?:
Geology, v. 24 p. 3-6.
Pratson,
L.F., O'Grady, D.B., Sarg, J.F., and Syvitski, J.P.M., 2000, Categorizing
the morphologic variability of siliciclastic passive continental margins:
Geology, v. 28 p. 207-210.
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| Images |
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| Map
of the United States showing locations of images (white boxes). Red areas within
white boxes are regions depicted in images. Arrows indicate view direction.
Click inside white boxes to see images of each area. |
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A. Numerous, deep submarine
canyons cut by subsea avalanches occur off New Jersey, Delaware, and Maryland.
Click
here to view image at full size.
Click
here to see close-ups of particular areas.
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B. Groundwater seeping
from low-lying Florida weakens the deep seafloor off the West Florida coast,
periodically causing the slope to collapse, a process that over time has contributed
to the formation of a sheer, mile-high cliff.
Click
here to view image at full size.
Click
here to see close-ups of particular areas.
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C.
Movement of buried salt, driven by massive loading of sediments eroded from
the Rocky Mountains and delivered to the Louisiana coast by the Mississippi
River, has created a pockmarked, lunar-like seafloor off Louisiana.
Click
here to view image at full size.
Click
here to see close-ups of particular areas.
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D. A seascape of plateaus
and canyons reach out from the California coast where the North American Plate
is sliding past the Pacific Plate along a complex system of faults, including
the San Andreas Fault.
Click
here to view image at full size.
Click
here to see close-ups of particular areas.
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E.
Seafloor sediments are being piled up in ridges along the Oregon margin like
folds in a carpet as they are scraped off the Juan de Fuca Plate by the over-riding
North American Plate in a process called subduction.
Click
here to view image at full size.
Click
here to see close-ups of particular areas.
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| For
information on additional images contact Dr. William Haxby at Lamont-Doherty
Earth Observatory, Palisades, NY 10964, or at bill@lamont.ldeo.columbia.edu
. |
| Back
to Lincoln Pratson's home page |
| Back
to the Duke University Solid
Earth Home Page |
| Back
to the Duke University Surface
Processes Home Page |
 Return
to the EOS home page |
| All
images are copyrighted. |
| Last
updated November 19, 2001 |
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