New evidence deep beneath the Arctic ice suggests a series of underwater volcanoes have erupted in violent explosions in the past decade.

Hidden 2.5 miles (4,000 meters) beneath the Arctic surface, the volcanoes are up to a mile (2,000 meters) in diameter and a few hundred yards tall.

They formed along the Gakkel Ridge, a lengthy crack in the ocean crust where two rocky plates are spreading apart, pulling new melted rock to the surface.

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Until now, scientists thought undersea volcanoes only dribbled lava from cracks in the seafloor. The extreme pressure from the overlying water makes it difficult for gas and magma to blast outward.

But the Gakkel Ridge, which is relatively unexplored and considered unique for its slow spreading rate, is just the place for surprises.

Robert Reeves-Sohn of the Woods Hole Oceanographic Institution (WHOI) in Massachusetts and his colleagues discovered jagged, glassy fragments of rock scattered around the volcanoes, suggesting explosive eruptions occurred between 1999 and 2001.

They hypothesize that the slow spreading could allow excess gas to build up in pockets of magma beneath the oceanic crust. When the gas pressure gets high enough, it pops like a champagne bottle being uncorked.

With news this week that polar ice is melting dramatically, underwater Arctic pyrotechnics might seem like a logical smoking gun.

Scientists don't see any significant connection, however.

"We don't believe the volcanoes had much effect on the overlying ice," Reeves-Sohn told LiveScience, "but they seem to have had a major impact on the overlying water column."

The eruptions discharge large amounts of carbon dioxide, helium, trace metals and heat into the water over long distances, he said.

The research, detailed in the June 26 issue of the journal Nature, was funded by NASA, the National Science Foundation and WHOI.

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