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Images: Unraveling the Tapestry of Ocean Crust

In a few places on Earth, blocks of oceanic crust (called ophiolites) have been thrust onto the continents, giving scientists the unusual chance to get a firsthand look at rock formations that were once beneath the seafloor. The largest ophiolite is in Oman near the Persian Gulf. (Photo by Peter Kelemen, Woods Hole Oceanographic Institution )

WHOI scientists Peter Kelemen (top arrow) and Greg Hirth (about 50 meters directly below) are walking on rocks that once were in the upper mantle beneath the seafloor. In this photomosaic of a mountainside in Oman (and in photo on above), light-colored rocks (dunite) are ancient channels through which melt once flowed through the mantle. (Mike Braun, WHOI.)

A computer model simulating the location of channels formed by localized melt flow in the mantle provides this picture: The melt dissolves minerals in rock minerals to form small porous channels that subsequently coalesce into larger ones. Similar flow patterns may be at work in other natural systems. (Marc Spiegelman/Lamont-Doherty.)

By studying how water flows on a beach, scientists can make parallels with the flow of magma beneath the seafloor. On a beach, small water channels flowing downhill erode sand in front of them and coalesce into one larger channel. But when the slope decreases downstream, the flow slows down. Sand grains that were carried in suspension begin to become deposited, creating a barrier that block the flow. Smaller channels begin to diverge again. (Peter Kelemen.)