Volcanic eruptions fire Arctic ice bottoms

June 26th, 2008 - 4:12 pm ICT by IANS  

Washington, June 26 (IANS) Volcanic eruptions deep below the icy bottom of Arctic Ocean are spewing splintered, fragmented rock, even though intense weight and pressure of water rules them out in theory. Researchers led by Woods Hole Oceanographic Institution (WHOI) found jagged, glassy rock fragments spread out over a 10 square km area around a series of small craters about four kilometres below the sea surface.

The volcanoes lie along the Gakkel Ridge, a remote and unexplored section of the mid-ocean ridge system that runs through the Arctic Ocean.

“These are the first pyroclastic (fragmented rock) deposits we have ever found in such deep water, at oppressive pressures that inhibit the formation of steam… thought… not possible,” said WHOI geophysicist Rob Reves-Sohn, co-author and chief scientist of Arctic Gakkel Vents Expedition (AGAVE-2007).

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 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 to 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, reported EurekAlert.

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 Loke, Oden, and Thor.

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.

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

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