While investigating a mountain on the bottom of the Atlantic Ocean last week, scientists made a serendipitous discovery: a field of up to 60-meter-high columns releasing hot water--the largest ocean hydrothermal vents ever discovered. The crew of the research vessel Atlantis had not expected to find anything of the sort, but suddenly "amazing white structures" began looming on the video screen, according to the expedition's online journal.
Most hydrothermal vents formed during the cooling of volcanic rocks that form the shallow portion of the oceanic crust, near the mid-ocean ridges where upwelling magma creates the crustal plates. Some vents found in the Pacific, known as "black smokers," spew clouds of sulfur and iron-containing materials and host thriving communities of clams, shrimps, and other marine life.
These new vents, dubbed the "Lost City Field," are different, says geologist Deborah Kelley of the University of Washington, Seattle, one of the directors of the expedition. The vents are kilometers away from the mid-ocean ridges, and the escaping fluid doesn't seem to be heated by volcanic rocks. Instead, the vent field sits atop peridotite, a magnesium-rich silicate rock that's usually found in the mantle. Unlike vents that sit atop iron-rich volcanic rock, tests show that the vents contain large amounts of carbonate, and Kelley thinks the vents contain calcium and magnesium as well. The columns are largely devoid of marine life, except for microbes.
Other researchers are also puzzling over the Lost City Field's origin. The vents are "not very hot, but there still must be a mechanism for how they are formed" in an area not affected by volcanic eruptions, says Susan Humphris, a geologist at the Woods Hole Oceanographic Institution in Massachusetts.