More than 1,800 feet beneath the Pacific Ocean, the eruptions of an undersea volcano have revealed themselves on film, including the ejection of glowing red lava and the sounds of exploding gases.
"It's the first place where we've been able to observe an active volcanic eruption underwater," said Bill Chadwick of the Oregon State University Hatfield Marine Science Center in Newport, who led the group that observed the volcano with a remotely operated vehicle.
"Even though we think about 75 percent of the world's volcanic activity happens underwater in the ocean basins, it's a lot harder to see and detect."
The team identified the site after scanning the water in the region with an instrument that detects hydrothermal plumes -- water columns that bear the signature of volcanic activity below.
"This site had really unusual chemistry, so that's what put it high on our priority list when we went back to do the dives," Chadwick said.
There are advantages to studying volcanoes deeply underwater, he said.
"The pressure subdued the explosive activity so we could get really close with the vehicle without endangering it," said Chadwick, "and we could watch the activity for an hour at a time, which is not something you can do on land with a volcano exploding in your face."
Rocks thrown up and out of the volcano land gently after tumbling through water, and the water quickly cools the hot lava and gases.
"Underwater, you can see the gases a lot easier," he added. "So we can have a much clearer view of what's going on. In air, gases are hard to see."
The team used these observations to estimate the ratio of gases to lava erupting.
"It's lots of gas and not much lava," said Chadwick. "The gas is the main thing driving these eruptions."
The team made the recordings in April 2006 at a place called Brimstone Pit, about 60 miles north of Guam at a subduction zone, where one tectonic plate plunges beneath another. They recently published their results online in the Journal of Geophysical Research.
This was the team's third expedition to the pit, which was erupting each time, but on the last visit the pit opening was unobstructed -- the team believes they arrived just after it had collapsed -- allowing unprecedented views of the eruptions. It was also the first time they were able to record the sounds, mostly created by the gases, that accompanied the eruptions.
"We could link the two, so now we know what the sounds mean visually," Chadwick said.
The team left a sound recorder near the site earlier this year. They will return to retrieve data from the recorder in the fall.
Because they now know how the sounds correspond to their observations, they will be able to trace what happened over the six-month period through sound, to get a better idea how Brimstone Pit erupts over longer periods of time.
"It's really excellent work," said Daniel Fornari of Woods Hole Oceanographic Institution in Woods Hole, Mass. "It's a unique opportunity for us to be able to study these types of processes. Normally with explosive volcanism, if you're there, you're going to be dead."
"Most of the geology that we probably eventually see, a large part of that has happened underwater," said Michael Perfit, a marine geologist at the University of Florida in Gainesville. "We have to look backwards and try to figure out how it happened. By looking at this, you get a sense of how these very important processes take place."
The team will return with the remotely operated vehicle next spring to make more visual observations. But the last expedition could be hard to top.
"It was really exciting that we could see glowing lava at times. To glow like that it has to be above about 700 degrees C [almost 1300 F]." Chadwick said. "Every day there was something new to see. It was the most exciting cruise I've ever been on for sure."
Underwater Volcano Caught on Film: Discovery News : Discovery Channel
