Washington, June 26 : An international team of researchers has provided evidence of explosive volcanism in the deeps of the ice-covered Arctic Ocean for the first time.
The researchers were led by the American Woods Hole Oceanographic Institution (WHOI) to an expedition to the Gakkel Ridge in the Arctic Ocean.
With a specially developed camera, they discovered extensive layers of volcanic ash on the seafloor, which indicates a gigantic volcanic eruption.
"Explosive volcanic eruptions on land are nothing unusual and pose a great threat for whole areas," explains Dr Vera Schlindwein of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association.
According to Robert Reves-Sohn, staff member of the WHOI and lead scientist of the expedition carried out on the Swedish icebreaker Oden in 2007, "So far, researchers have assumed that explosive volcanism cannot happen in water depths exceeding 3 kilometres because of high ambient pressure."
"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," he added.
The Gakkel Ridge in the Arctic Ocean spreads so slowly at 6-14 mm/year, that current theories considered volcanism unlikely, until a series of 300 strong earthquakes over a period of eight months indicated an eruption at 85° N 85° E in 4 kilometres water depth in 1999.
Scientists of the Alfred Wegener Institute became aware of this earthquake swarm and reported about its unusual properties in the year 2000.
Vera Schlindwein and her junior research group are closely examining the earthquake activity of these ultraslow-spreading ridges since 2006.
"The Gakkel Ridge is covered with sea-ice the whole year. To detect little earthquakes, which accompany geological processes, we have to deploy our seismometers on drifting ice floes," she said.
According to Vera, "Our endeavours now concentrate on reconstructing and understanding the explosive volcanic episodes from 1999 and 2001 by means of the accompanying earthquakes."
"We want to know, which geological features led to a gas pressure so high that it even enabled an explosive eruption in these water depths," she added.