Lucky break gives scientists unique view of underwater eruption

The eruption, which took place early this spring thousands of feet below the surface of the Pacific Ocean, is described in a paper set for release Thursday in Science Express, the journal Science’s online magazine.

“Never before have we had instruments in place like this that recorded an eruptive event on the seafloor,” said Mike Perfit, a UF professor of geology.

Perfit was among the scientists who visited the eruption shortly after it took place aboard the deep-sea submersible Alvin. The project was headed by Maya Tolstoy, a seismologist with Columbia University’s Lamont Doherty Earth Observatory and the lead author of the Science paper.

Perfit said the eruption occurred about 400 miles west of Mexico along a massive volcanic mountain range called the East Pacific Rise. Fortuitously, it was one of three active undersea volcanic areas that were selected for high-intensity research in the late 1990s as part of the National Science Foundation’s RIDGE research program. As a result, geologists, biologists, geophysicists and other specialists had gathered a storehouse of samples, data and photos from the site.

The scientists also had numerous instruments in place on the ocean bottom 8,000 feet below the surface – including a dozen “ocean bottom seismometers.” These devices listen for and measure seismic activity which is recorded on a small computer hooked to a buoyant sphere. Seismologists on the research vessel retrieve the instrument by electronically signaling the seismometer to release from the seafloor, which then carries the hard drive full of data to the ocean surface.

When a group of scientists visited the East Pacific Rise site in April on a routine mission to retrieve the seismometers, they were surprised to discover that only four detached and rose to the surface, Perfit said. Three others responded to scientists’ signals but refused to bob to the surface. “They were responding, but they weren’t coming up. Usually you might lose one, but you don’t lose that many of your ocean bottom seismometers,” Perfit said.

Intrigued, the scientists used onboard equipment to measure temperature, salinity and turbidity near the ocean bottom. They discovered the water was unusually cloudy and warm above the ridge crest, indicating a possible eruption. To confirm it, the scientists retrieved some ocean floor lava from the ocean floor. Subsequent tests by Perfit and K. Rubin, a colleague at the University of Hawaii, confirmed that the rock was formed very recently as the result of a deep sea volcanic eruption.

Scientists in the RIDGE Program quickly mobilized and sent another ship to the site equipped with a deep-diving camera system. Towed behind the ship, the cameras revealed “brand new black glassy lava,” Perfit said. Unlike the explosive lava-spewing volcanoes on Earth’s surface, deep sea volcanoes emit lava slowly because of the enormous ocean pressure. This lava forms pillow-like structures across the ocean bottom as it seeps out of seafloor fissures.

The cameras also failed to record any visible ocean bottom life with the exception of thick white masses of bacterial colonies that coated the lava. That was in sharp contrast to thriving life recorded at the site in the years before. “There was at least one site that was a lush site with tubeworms, crabs and mussels and it was just gone, just buried,” Perfit said.

Perfit was among the scientists aboard the submersible Alvin who did repeated dives along the site in June and July. Among other things, the group located the ocean bottom seismometers and quickly discovered the problem – they had become enveloped and trapped in the lava flow.

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

That in turn will lead to much greater understanding of the unique underwater phenomena. For example, next April scientists, including Perfit, hope to retrieve some of the seismometers because they are likely to contain new information about the seismic activity leading up to and during the eruption — and possibly predict these events. “We’ll be lucky if we catch another event like this in my lifetime,” Perfit said. “It really revitalizes the field.”