The first deep sea vent was found in 1977 near the Galapagos Islands by Earth scientists in the ALVIN, a small research submersible. But ALVIN moves very slowly and costs $20,000 a day to operate, and time at sea is limited. The odds of finding a vent by chance, as those scientists did, are less than one in a million.

Instead, scientists at the surface use indirect methods to locate vents by looking for the large plume of warmer water that indicates a vent below. Because the plume is much larger than the vent, scientists have a better chance of detecting the plumes and then tracing it back to a vent, even if their ship has passed over the actual opening in the seafloor.

Click the image for an enlarged version that includes a list of hydrothermal site locations.