Extreme locations on Earth continue to contain surprises. The latest comes from a ridge in the Arctic Ocean. Gakkel Ridge is the world's slowest "spreading center," a place where the ocean floor pulls apart and magma rises up to form new crust. Now a team of researchers has discovered that Gakkel Ridge has a surprising excess of volcanic and hydrothermal activity.
Midocean ridges are like two conveyer belts running in opposite directions. As a pair of adjacent crustal plates pull apart, magma and hot, viscous, but still solid rock well up into the rift. They cool, spreading out as new seafloor. Because the rising rock has longer to cool as it travels up beneath slow spreading ridges, these rifts should produce less magma and thinner crusts.
So researchers on a cruise through the Arctic ice were surprised to find volcanoes and hydrothermal vents on the Gakkel Ridge, which spreads just 5% as fast as the quickest ridges. In the easternmost portion, the team found mountain-sized volcanic cones. The cones were scattered over the ridge, rather than built up into a continuous range, as on fast ridges. This finding indicates that magma might be concentrated--enough to give off heat to make hydrothermal water plumes in the area, which also occur more than expected. Another oddity is that the middle stretch of the ridge has no volcanism whatsoever. These surprising results are reported in two papers in the 26 June issue of Nature. "We'll be using these samples for years to come to get ideas of how midocean ridges work," says Peter Michael, a geophysicist at the University of Tulsa in Oklahoma and a member of the team.
"This is the most exciting oceanographic expedition to take place in the past decade," says Emily Klein, a geochemist at Duke University in Durham, North Carolina. The ridge's sandwich effect of volcanic, then nonvolcanic, then volcanic regions "was one of the things that was a big surprise," she says, adding that researchers are still trying to figure out the dynamics behind the odd activity.