Beneath the waves of the South Pacific lies a volcanic realm nearly as strange as that featured in TV's hit drama Lost.

But instead of a mysterious island, scientists have found a bubbling submarine volcano whose weird features include a swirling vortex, a host of strange animals, and a fearsome zone of toxic waters dubbed the Moat of Death.

The volcano, described in this week's online edition of the Proceedings of the National Academy of Sciences, sits within the crater of a gigantic underwater mountain rising more than 4,500 meters (15,000 feet) from the ocean floor near the island of Samoa (see map).

The seamount, called Vailulu'u, is an active volcano, with a 2-mile-wide (3.2-kilometer-wide) crater. The cone rising within it has been dubbed Nafanua, for the Samoan goddess of war.

Volcano Teeming With Life

Five years ago Hubert Staudigel of the Scripps Institution of Oceanography in La Jolla, California, and his colleagues mapped the mountain using remote-sensing techniques.

When they returned to the site in 2005 for a more thorough study with submersible vehicles, the scientists found that the seamount had grown a new, 300-meter (1,000-foot) lava cone, a sign of renewed volcanic activity.

The peak of the cone, 700 meters (2,300 feet) below sea level, turned out to be teeming with life.

"It was just full of eels," Staudigel said.

"When we sent the submersible down, we found hundreds of eels scurrying out of the rock. Normally you'd see one or two."

"That's very spectacular," he continued, "because there's not much food at that depth. You wonder what the eels live off of."

At first the scientists thought the eels were eating microbes that lived near the cone's volcanic vents. But when some of the eels were caught, their stomachs turned out to be full of shrimp.

That raised a new question: Where did the shrimp come from?

The researchers found that the huge seamount interacts with tides and ocean currents to create a vortex in which water rises along the outside of the mountain and then descends into its interior.

The descending water is likely bringing shrimp to the eels, allowing them to thrive in such large numbers.

Another member of the team, Craig Young, a biologist with the Oregon Institute of Marine Biology in Charleston, is intrigued by how the eels have taken advantage of a quirk of oceanography.

"The eels have selected a place there where the currents are concentrating food," he said.

But the scientists are even more intrigued by a region called the Moat of Death.

Moat of Death

The moat lies between Vailulu'u's encircling crater and the rim of the cone inside it.

It's an extremely toxic environment, Staudigel said, where oxygen levels are dangerously low and volcanic vents fill the water with iron soot "almost like underwater smog."

The volcano is also spewing liquid carbon dioxide, which combines with seawater to make a deadly acidic mix.

And the same currents that bring shrimp to the eels also bring fish into the toxic moat, trapping them.

The result? "We find one fish carcass after another," Staudigel said.

But one species survives within the moat, a type of sea worm that seems to be feeding on the animal carcasses.

It's not clear how the worms manage to live in a region where nothing but bacteria can live.

Jim Barry, a deep-sea biologist with the Monterey Bay Aquarium Research Institute in Moss Landing, California, is impressed by the volcano find.

"This is a new habitat," he said.

And it's potentially important for future study, he added, because by trapping carbon dioxide in the moat, this habitat provides scientists with a way to study what the oceans of the not-so-distant future may be like.

As levels of carbon dioxide continue to rise, due to the combustion of fossil fuels, deforestation, and other causes, much of the gas will inevitably wind up in the sea, he explained.

"We're going to see big changes in the chemistry of the ocean in the next 200 years," Barry said.

"Systems like this will give us a great deal of information about what we might expect in the future."

• National Geographic News