Five hundred vents newly discovered off the U.S. West Coast, each bubbling methane from Earth's belly, top a long list of revelations about "submerged America" being celebrated by leading marine explorers meeting in New York. "It appears that the entire coast off Washington, Oregon, and California is a giant methane seep," says RMS Titanic discoverer Robert Ballard, who found the new-to-science vents on summer expeditions by his ship, Nautilus.

The discoveries double to about 1,000 the number of such vents now known to exist along the continental margins of the U.S. This fizzing methane is a powerful greenhouse gas if it escapes into the atmosphere; a clean burning fuel if safely captured. "This is an area ripe for discovery," says Dr. Nicole Raineault, Director of Science Operations with Dr. Ballard's Ocean Exploration Trust. "We do not know how many seeps exist, even in U.S. waters, how long they have been active, how persistent they are, what activated them or how much methane, if any, makes it into the atmosphere."

Further research and measuring will help fill important knowledge gaps, including how hydrocarbons behave at depth underwater and within the geological structure of the ocean floor. Expeditions this year include NOAA's Deepwater Exploration of the Marianas Trench – a 59-day voyage with 22 dives into the planet's deepest known canyons in the Pacific Ocean near Guam.

NOAA explorers added three new hydrothermal vents to the world's inventory and a new high-temperature "black smoker" vent field composed of chimneys up to 30 meters tall – the height of a nine-story building. Also revealed: a tiny spot volcano (the first ever discovered in U.S. waters), a new mud volcano, thick gardens of deep-sea corals and sponges, a rare high-density community of basket stars and crinoids (a living fossil), and historic wreckage from World War II.

Scores of spectacular, rare, and sometimes baffling unknown species encountered on this year's voyages to new deep ocean areas include a bizarre purple "mud monster" and a mysterious purple disco-ball-like orb as well as a swimming purple sea cucumber and a rare purple Vampire Squid.