Dive and Discover : Exp. 8 : Juan de Fuca Ridge : Daily Updates

Earth’s surface is broken into 12 major plates

, giant rafts of crust

floating over the mantle

like chunks of ice in the sea. These plates measure 60 to 75 miles (100 to 120 kilometers) thick, and comprise the planet’s crust and a small part of the upper mantle. Many plates contain both continental and oceanic crust.

The largest plate, the Pacific plate, stretches from Alaska beyond New Zealand to the Southern Ocean, and from Baja, California to Guam. Like other plates, it creeps continuously about as fast as your fingernails grow. The edges of the plate host earthquakes and volcanoes, which some scientists onboard Atlantis are working to understand.

Much of this cruise to the Endeavour Segment has been near a center of seafloor spreading

, or a boundary where the Pacific and Juan de Fuca plates separate. For the remainder of the cruise, beginning Saturday, researchers will concentrate their work on a type of boundary

called a transform fault

. At transform faults, plates grind past each other in opposite directions. Powerful earthquakes often strike along these boundaries.

On Friday night we will travel 95 nautical miles northeast to Nootka, a transform fault off the west coast of Vancouver Island, Canada. Each year, an average of 80 earthquakes are recorded there, said Deb Kelley, the expedition’s chief scientist.

Several scientists on Atlantis will study how earthquakes impact fluids that flow in and out of the seafloor. Others will test instruments at Nootka that they hope to use for future research expeditions on cold-water seeps from the seafloor.

After this expedition, Geochemist Dave Hilton plans to visit the western coast of Central America, part of his research on the cycling of carbon and helium gases. Nootka is a good place for Dave and colleague Kevin Brown, both of the Scripps Institution of Oceanography, to test instruments deployed off the coast of El Salvador, Honduras, Nicaragua, Guatemala, and Costa Rica. The cold seeps at Nootka resemble flows found in these areas of Central America, and allow for realistic testing and development of new techniques and instruments.