The best characterized of these hydrothermal vents occur at various intervals along a tectonic plate's new-forming edge, known as a spreading zone. Earth's mid-ocean ridge is one near-continuous zone of spreading seafloor.

A spreading zone can be considered a "linear volcano" with vent holes occurring at various points along its meandering crest, explains Baker, an oceanographer at the National Oceanic and Atmospheric Administration's Seattle lab.

Their sophisticated equipment turned up direct evidence of three new hydrothermal vents in that spreading zone and indirect evidence--hydrothermal plumes--of several more.