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Under the Sea: Exotic New Landscapes

December 1996

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 images.

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 variety.

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 cables.

The images created by the Lamont-Doherty team can be viewed on the World Wide Web at http://www.ldeo.columbia.edu

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