Under the Sea: Exotic New Landscapes
Off the coast of Oregon and under more
than a mile of water, lies one of Earth's active seams--a
place where two crustal plates come together in an amazing
display of tectonic energy.
The North American Plate is riding roughshod over the Juan
de Fuca Plate, pushing it down into the earth's interior, and
in the process, scraping up sea floor sediments like a bulldozer
and leaving them in piles.
"It looks like folds in a carpet," says Lincoln Pratson, geologist
at the University of Colorado and the National Oceanic and
Atmospheric Administration (NOAA). The computer-generated picture
of Oregon's seascape is one of several views of continental
margins that Pratson and his colleague William Haxby studied
while they both were at the Lamont-Doherty Earth Observatory.
Collection of the data used in creating these pictures began
in 1983 when President Ronald Reagan declared that the nation's
boundaries extended for 230 miles off any U.S. shore. The U.S.
Geological Survey performed the general mapping of this new
part of the country, while NOAA and scientists supported by
NSF used multi-beam, echo-sounding systems to get high resolution
Using several data sets, Pratson and Haxby evaluated the continental
margins at each of five survey sites. Not only do their results
describe the slope of the continental margin in more detail
than had ever been known, but their pictures show a nearby
world that's very different from the one above.
"The images show that the sea floor off the U.S. coast is
as remarkable and in some ways as alien as landscapes we've
seen on Mars or Venus," says Pratson.
With a starkness characteristic of the photography of Ansel
Adams, the pictures show the naked forces of geology. Tectonics,
sedimentation, and lithology (the structure and composition
of rocks) have all been stripped of trees, grasses, and other
appendages of land, revealing their raw power and unexpected
For example, the site off the western coast of Florida contrasts
sharply with its nearby state. Instead of Florida's uniform,
gentle slopes, the continental margin has sharp edges and mile-high
cliffs that drop to the abyss below.
Near Louisiana the dominant force is movement of buried salt.
The continental margin is a pockmarked, lunaresque sea floor
that started when the Gulf of Mexico was dry and filled with
evaporated sea salt. The salt was then covered by the mud from
the Mississippi, and, when the sea returned, the salt was squeezed
into strange shapes by the weight of the sediments.
Aside from their beauty, the images and the accompanying analysis
may provide new tools in the study of ocean floors. But more
immediately, Pratson suggests, the images will assist companies
considering gas or oil exploration and those laying transcontinental
The images created by the Lamont-Doherty team can be viewed
on the World Wide Web at http://www.ldeo.columbia.edu