Seafloor volcanic eruption recorded

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A team of scientists working in the Pacific Ocean has recorded a volcanic eruption 8,000 feet below the surface, which, for the first time, documents what happens before, during and after such events.

"Never before have we had instruments in place like this that recorded an eruptive event on the seafloor," said Mike Perfit, a professor of geology at the University of Florida and an author of a report published yesterday in the online journal Sciencexpress.

"We have seen ... eruptions before, but we had never been there to monitor them like this," Mr. Perfit said. "We'll be lucky if we catch another event like this in my lifetime."

The eruption occurred early this spring about 400 miles west of Mexico along a massive volcanic mountain range called East Pacific Rise.

The area observed is part of what is known as the global mid-ocean ridge system, described as the largest single volcanic feature on Earth. Mid-ocean ridges are places where the Earth's tectonic plates are gradually moving apart. Beneath a mid-ocean ridge, mantle material partially melts as it rises in response to reduced pressure.

As the Earth's plates move apart, this melted rock, or magma, rises to fill the gap, sometimes leading to volcanic eruptions beneath the ocean.

In the report, lead author Maya Tolstoy of Columbia University's Lamont-Doherty Earth Observatory and colleagues note that "two-thirds of the Earth's surface is formed at mid-ocean ridges." It is there that the Earth's crust spreads, creating new ocean floor and renewing the planet's surface.

But until now, these processes have been "poorly understood because they occur far beneath the ocean surface," according to the report.

Better understanding occurred as a result of this research, funded by the National Science Foundation, as part of its Ridge 2000 Program. East Pacific Rise was one of three active undersea volcanic areas NSF selected for closer observation as a result of volcanic action that occurred there in 1991-92.

Geologists, seismologists, biologists, geophysicists and hydrologists involved in Ridge 2000 had gathered extensive samples, data and photographs from the site. They also had many instruments in place on the ocean floor, including a dozen seismometers that monitor and measure seismic activity.

In April, Miss Tolstoy and others went to the site to retrieve the seismometers. When only a third of the devices responded as they should have, the scientists suspected something was awry.

Using equipment to measure temperature, salinity and turbidity near the ocean bottom, they found the water was unusually cloudy and warm above the ridge crest, which suggested a possible eruption. They confirmed an eruption had occurred by retrieving lava from the ocean floor.

Mr. Perfit was aboard a submersible vessel that made repeated dives at East Pacific Rise in June and July. He said the introduction of a new fiber-optic deep-diving camera system revealed "brand new black glossy lava."

Mr. Perfit and his group also discovered the missing seismometers on the ocean bottom and determined why they had not functioned properly -- they had been trapped in a lava flow. He plans to retrieve them during a mission in April.

The eruption allows scientists an unprecedented view of the "death and birth of a mid-ocean ridge from all perspectives -- geological, biological, geophysical," Mr. Perfit said.