CTD plume hunters at work. l to r: John Lupton, Nick Dyriw, Jelena Puzic, Ed Baker, Marv Lilley, Joe Resing.
Bathymetry of the area where a massive volcanic eruption is suspected.

2008 Expedition to Lau Basin

November 21, 2008

Still a week from Thanksgiving, and we are already stuffed with so much new information we feel like we can’t digest another byte. For three days now we have been tracking down evidence for what we suspect is a massive volcanic eruption that has propelled ash particles as high as a kilometer above the seafloor. We came expecting to explore this midocean ridge segment simply for undiscovered hydrothermal vent sites. These hot springs are like an underwater Yellowstone, discharging water as hot as 700°F and supporting amazing ecosystems that thrive on poisonous gases, such as hydrogen sulfide (that “rotten egg” smell). We target their location by mapping the plumes of chemicals and particles that rise from them like campfire smoke.

We found far more of these plumes than expected, and far higher above the seafloor than normally seems reasonable. Two suspects were readily identified: astride the ridge are two small volcanoes, Maka (Tongan for “rock”) and Tafu (“source of fire”). Tafu, the larger of the two, rises some 500 m above the ridge (to a depth of about 1400 meters), and so was our first candidate. We lowered instruments over the side and down through the water above the summit. Scientists, glued to monitors like kids to video games, were disappointed by scant evidence of activity. Maka, 150 meters less high, was next. The verdict so far seems rock-hard. Beginning at the unbelievable depth of only 700 meters (shallow to oceanographers!) the first plume jumped onto the monitors. Then layer after layer, each chemical rich, some thick, some thin, until the instruments stopped just a few meters above Maka’s summit at 1560 meters, a mile deep. We had just documented a display of submarine volcanic might that few scientists have ever witnessed.

The surging activity at Maka had us wondering if erupting lava might also be leaking out on the deeper ridge. We answered that question with some dangerous work, towing fragile instruments at the end of a 3-kilometer-long cable, only 20 meters above the rocky bottom. At a shallow spot on the ridge we found evidence of warm fluids percolating up through the rocks. The chemistry of our water samples suggests that these fluids could be warmed by a very recent—days or weeks?—eruption of lava onto the seafloor.
Many mysteries still remain, and we will be working on them for the rest of the cruise, and then at home in our laboratories. One we may never figure out. Why are we calling the erupting volcano the “rock” rather than the “source of fire”?

Ed Baker, Hydrothermal Plume Studies

updated 1/14/2009