A research team led by the Woods Hole Oceanographic Institute (WHOI) has found evidence of explosive volcanic eruptions deep under the ice-covered surface of the Arctic Ocean. Violent eruptions were not thought possible at great ocean depths because of the intense weight and pressure of water.

Researchers found jagged, glassy rock fragments, known as pyroclastic deposits, spread out over a 10 square kilometer (4 square mile) area around a series of small volcanic craters about 4,000 meters (2.5 miles) below the sea surface. The volcanoes lie along the Gakkel Ridge, a section of the mid-ocean ridge system that runs through the Arctic Ocean.

Scientists had thought it was unlikely explosive plumes of gas, steam and rock would rise from volcanoes submerged under miles of cold water. From earlier observations of seafloor samples, the researchers doubted that the undersea volcanoes below 3,000 meters (1.8 miles) could build up the amount of steam and carbon dioxide gas in the magma to throw a mass of rock up in the water column. 

The researchers used survey instruments, cameras, samples of rock and sediment, and videos to study the volcanic craters. They found evidence that rock debris had fallen out of the water rather than being moved around by lava. Fresh pyroclastic deposits were spread out in all directions from the volcanic craters.

The researchers say more needs to be done to determine whether pyroclastic eruptions are common or whether they only occur along the Gakkel Ridge.

At the Woods Hole web site you can see images of the seafloor along the volcanoes as well as a fly-through animation showing bathymetry (depth measurements) of the Gakkel Ridge.