Some of the peaks tower nearly 10,000 feet (3,000 meters) above the ocean floor — nearly tall enough to break the water's surface.
"That's a big volcano. That's a very big volcano. If that was on land it would be quite remarkable," said Philip Leat, a vulcanologist with the British Antarctic Survey who led a seafloor mapping expedition to the region in 2007 and 2010.
The group of 12 underwater mountains lies south of the South Sandwich Islands — desolate, ice-covered volcanoes that rise above the southern Atlantic Ocean about halfway between South America and South Africa and erupted as recently as 2008. It's the first time such a large number of undersea volcanoes has been found together in the Antarctic region.
Leat said the survey team was somewhat surprised by the find.
"We knew there were other volcanoes in the area, but we didn't go trying to find volcanoes," Leat told OurAmazingPlanet. "We just went because there was a big blank area on the map and we had no idea what was there; we just wanted to fill in the seafloor."
The team did so, thanks to ship-borne seafloor mapping technology, and not without a few hair-raising adventures.
Leat said the images of the seafloor appear before your eyes on screens as the ship moves through the water. "So it's very exciting," he said. "You go along and suddenly you see the bottom start to rise up underneath you, and you don't know how shallow it's going to get."
At one point, in the dead of night, the team encountered a volcano so large it looked as though the RRS James Clark Ross, the team's research vessel, might actually crash into the hidden summit. "It was quite frightening, actually," Leat said.
The researchers stopped the ship and decided to return in daylight. The onboard instruments revealed that some of the peaks rise within 160 feet (50 meters) of the ocean's surface.
Though the peaks are largely invisible without the aid of 3-D mapping technology, scientists can tell they're volcanoes.
Leat said their conelike silhouette is a dead giveaway. "There's no other way of getting that shape on the seafloor," he said. In addition, the researchers dredged up rocky material from several peaks and found it rife with volcanic ash, lumps of pumice and black lava.
The find backed up reports from a ship that visited the area in 1962, which indicated a hidden volcano had erupted in the region.
Leat's biologist colleagues discovered some interesting creatures living in the hot-spring-like conditionsnear the underwater mountains, and news on that will be forthcoming, Leat said.
Despite the frozen, isolated conditions, Leat said the expeditions were far from boring. Quite the opposite, in fact. Each moment, a hidden world never before seen by humans unfolded before their eyes.
"It's amazing," Leat said, "and you can hardly go to bed at night because you want to see what's happening."