News Release : Geologists Discover Signs of Volcanoes Blowing their Tops in the Deep Ocean Evidence of Violent Eruptions on Gakkel Ridge in the Arctic Defies Assumptions about Seafloor Pressure and Volcanism Printer-friendly E-mail to a friend

June 26, 2008
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	Enlarge Image A detailed bathymetric map shows the shape of the seafloor along the Gakkel Ridge in the Arctic Ocean. (Map courtesy of Martin Jakobsson (Stockholm University), Robert Reves-Sohn and Adam Soule (Woods Hole Oceanographic Institution) and the AGAVE science team)
	Enlarge Image Approximately 10 centimeters of pyroclastic deposits cover high-standing pillow lavas, indicating that the material was ejected from the volcano and settled through the water column onto the seafloor. (Photo courtesy of Rob Reves-Sohn, Hanumant Singh, Tim Shank, Susan Humphris, and William Lange, Woods Hole Oceanographic Institution, and the AGAVE science team)
	Enlarge Image In a WHOI laboratory, geophysicist Rob Reves-Sohn (left), geologist Adam Soule, and graduate student Claire Willis analyze samples of seafloor deposits brought back from the Gakkel Ridge. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)
	Enlarge Image These glassy, granular fragments of basalt were a key piece of evidence that volcanoes along the Gakkel Ridge have exploded violently. (Photo by Adam Soule and Claire Willis, Woods Hole Oceanographic Institution)
	Related Multimedia
	The CAMPER underwater vehicle captured these first-ever images of the seafloor along the Gakkel Ridge. Tim Silva, WHOI » View Video (Media Player) » View Video (Ipod Compatible) Fly-through animation showing bathymetry of the Gakkel Ridge 82 to 85E » View Video (Media Player)
	Related Links
	» Explosive volcanism on the ultraslow-spreading Gakkel Ridge from the journal Nature » Explorers Use New Robotic Vehicles to Hunt for Life and Hydrothermal Vents on Arctic Seafloor » Arctic Voyage Tests New Robots for Ice-covered Oceans from Oceanus magazine » Earth’s Complex Complexion: Expeditions to remote oceans expose new variations in ocean crust from Oceanus magazine » Who is Rob Reves-Sohn? » Scientists Report New Type of Mid-Ocean Ridge in Remote Parts of the Earth » Polar Discovery Expedition 2 - Arctic Gakkel Vents » Dive and Discover Expedition 11: Voyage to the Gakkel Ridge

A research team led by the Woods Hole Oceanographic Institution (WHOI) has uncovered evidence of explosive volcanic eruptions deep beneath the ice-covered surface of the Arctic Ocean. Such violent eruptions of splintered, fragmented rock—known as pyroclastic deposits—were not thought possible at great ocean depths because of the intense weight and pressure of water and because of the composition of seafloor magma and rock.

Researchers found jagged, glassy rock fragments 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 remote and mostly unexplored section of the mid-ocean ridge system that runs through the Arctic Ocean.

“These are the first pyroclastic deposits we've ever found in such deep water, at oppressive pressures that inhibit the formation of steam, and many people thought this was not possible,” said WHOI geophysicist Rob Reves-Sohn, lead author and chief scientist for the Arctic Gakkel Vents Expedition (AGAVE) of July 2007. “This means that a tremendous blast of CO₂ was released into the water column during the explosive eruption.”

The paper, which was co-authored by 22 investigators from nine institutions in four countries, was published in the June 26 issue of the journal Nature.

Seafloor volcanoes usually emit lobes and sheets of lava during an eruption, rather than explosive plumes of gas, steam, and rock that are ejected from land-based volcanoes. Because of the hydrostatic pressure of seawater, ocean eruptions are more likely to resemble those of Kilauea than Mount Saint Helens or Mount Pinatubo.

Making just the third expedition ever launched to the Gakkel Ridge—and the first to visually examine the seafloor--researchers used a combination of survey instruments, cameras, and a seafloor sampling platform to collect samples of rock and sediment, as well as dozens of hours of high-definition video. They saw rough shards and bits of basalt blanketing the seafloor and spread out in all directions from the volcanic craters they discovered and named Loké, Oden, and Thor.

They also found deposits on top of relatively new lavas and high-standing features—such as Duque’s Hill and Jessica’s Hill--indications that the rock debris had fallen or precipitated out of the water, rather than being moved as part of a lava flow that erupted from the volcanoes.

Closer analysis has shown that the some of the tiny fragments are angular bits of quenched glass known to volcanologists as limu o Pele, or “Pele's seaweed.” These fragments are formed when lava is stretched thin around expanding gas bubbles during an explosion. Reves-Sohn and colleagues also found larger blocks of rock—known as talus—that could have been ejected by explosive blasts from the seafloor.

Much of Earth’s surface is made up of oceanic crust formed by volcanism along seafloor mid-ocean ridges. These volcanic processes are tied to the rising of magma from Earth’s mantle and the spreading of Earth’s tectonic plates. Submerged under several kilometers of cold water, the volcanism of mid-ocean ridges tends to be relatively subdued compared to land-based eruptions.

To date, there have been scattered signs of pyroclastic volcanism in the sea, mostly in shallower water depths. Samples of sediment and rock collected on other expeditions have hinted at the possibilities at depths down to 3,000 meters, but the likelihood of explosive eruptions at greater depths seemed slim.

One reason is the tremendous pressure exerted by the weight of seawater, known as hydrostatic pressure. More importantly, it is very difficult to build up the amount of steam and carbon dioxide gas in the magma that would be required to explode a mass of rock up into the water column. (Far less energy is needed to do so in air.) In fact, the buildup of CO₂ in magma in the sea crust would have to be ten times higher than anyone has ever observed in seafloor samples.

The findings from the Gakkel Ridge expedition appear to show that deep-sea pyroclastic eruptions can and do happen. “The circulation and plumbing of the Gakkel Ridge might be different,” said Reves-Sohn. “There must be a lot more volatiles in the system than we thought.” The research team hypothesizes that excess gas may be building up like foam or froth near the ceiling of the magma chambers beneath the crust, waiting to pop like champagne beneath a cork.

“Are pyroclastic eruptions more common than we thought, or is there something special about the conditions along the Gakkel Ridge?” said Reves-Sohn. “That is our next question.”

Support for the Arctic Gakkel Vents Expedition and for vehicle development was provided by the National Science Foundation’s Office of Polar Programs; the NSF Division of Ocean Sciences; the Gordon Center for Subsurface Sensing and Imaging Systems, an NSF Engineering Research Center; the NASA Astrobiology Program; and the WHOI Deep Ocean Exploration Institute.

The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans’ role in the changing global environment.