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Underwater Eruptions Challenge Researchers

September/October 1998

Volcanologist Fred Duennebier arrived at Hawaii's underwater volcano, Loihi, only a few days after sensors said it had erupted.

The water was so turbid, so smoky, we couldn't see anything," he said, explaining that he went down in the submersible Pisces V while other researchers worked above. "But we knew something had happened because we found new rocks formed by a recent eruption." Samples included a piece of glass, fresh from its recent encounter with the geological furnace.

Robotic arm collecting samples; caption below

Sampling pillow lavas on Loihi with the Pisces V submarine; the robotic arm in the foreground is one of the manned-submersible’s manipulator arms. Collected samples are routinely brought to the laboratory for petrologic and geochemical analysis. Photo by Dr. Mike Garcia, University of Hawaii

Credit: Dr. Mike Garcia, University of Hawaii

Off the coast of Oregon, studying volcanoes on the Juan de Fuca Ridge isn’t any easier. A monitoring system of hydro-phones, tracked by an interagency group of researchers, helps pinpoint seismic events. Even then, researchers don’t have a map to a fresh lava spill. "Looking at the data, we don’t know for sure there has been an eruption," explains marine geochemist Jim Cowen, who, like Duennebier, is a professor at the University of Hawaii. "But the characteristics of the seismicity show that there could have been an eruption."

What the researchers actually see are earthquake swarms—many earthquakes in a small area. These swarms are often precursors of eruptions, signals that the molten rock is moving. After three swarms and three confirmed eruptions, researchers are fairly certain of the signal. In response, a swarm of scientists quickly pull together the equipment, personnel and funding to get a closer look at an underwater eruption.

At NSF, these rapid-response trips go through the full review process but are turned around in less than a week. Speed is important, explains David Epp, director of NSF's Marine Geology and Geophysics Program. "Everything changes quickly. A lot of heat and a lot of different chemicals and microbes are thrown into the water column; the signals can change in a matter of days, or even hours."

Once at sea, cruise teams work quickly to measure and sample the water column to determine if a large volume of hot water, called an event plume, has been released from the seafloor. When the event plume is located, researchers calculate its size, determine its chemical and biological characteristics, and release drifter buoys to trace the plume's motion. The researchers also take photographs of the seafloor and samples of new lavas.

Less than a decade ago, researchers had no way of knowing where or when an underwater eruption was happening. Now, with the new monitoring systems, NSF scientists studying the Juan de Fuca Ridge are able to examine the rapidly changing geological, chemical and biological aspects associated with underwater eruptions. Cowen explains, "In an eruption, the world belches out these mysterious organisms from the Earth’s crust. Suddenly they're accessible. The rest of the time, there is almost no way of getting a good look at them."

In Hawaii, scientists are watching closely as Loihi builds the next Hawaiian island. Even in a place where volcanoes erupt yearly, if not monthly, Loihi's behavior remains a mystery, says Duennebier. "We know quite a lot about how volcanoes behave on the surface, but underwater, it is a different story."

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