Thursday, Nov. 27

Vents Program Personell and Colleagues at the Lau Basin, 2008

l to r: Ed Baker, Sharon Walker, Nick Dyriw, Peter Crowhurst,
Susan Merle, Joe Resing, Bob Embley, Tamara Baumberger,
John Lupton, Lucia Upchurch, Ron Greene, Jelena Puzic,

Marv Lilley, Gwen Hemery

John Lupton
November 27

Here we are on Thanksgiving Day, conducting our final water-column casts before starting our 16-hour drive into port in Apia, Western Samoa. This has been an interesting and productive expedition. All of the exploration work on this trip has been done within the waters of the Kingdom of Tonga. We began our work on the Mangatolo Triple Junction (MTJ, also called the Kings Triple Junction) in the western part of our survey area. A triple junction is an unusual feature where 3 different spreading plate boundaries come together at one point. In this case our plume surveys indicated that only the northern arm of the MTJ currently has strong hydrothermal activity. Then we moved to the west and began working on the Northeastern Lau Spreading Center (NELSC), which proved to be much more interesting. As described in our Nov. 21 blog entry, one of our first surveys along the NELSC detected a remarkable layering of plumes extending up to 600 meters above the seafloor. Since typical hydrothermal plumes rise less than 300 meters above the ocean floor, these high rising plumes had us puzzled. Furthermore, some of these plume layers contained very high concentrations of hydrogen gas, which suggested to us that a seafloor volcanic eruption was either occurring or had recently occurred. What was even more surprising was that we were not able to find these high rising plumes during later surveys over the same area. We finally decided we were dealing with a system that was constantly changing, instead of the usual steady input from a long-lived hot spring system. This is exactly what one would expect from a seafloor volcanic eruption.

After completing an initial survey of the NELSC, we adopted a strategy of making “sorties” to survey areas to the east and north, and then returning to the NELSC to re-sample the area of the purported seafloor eruption. Directly east of the NELSC the seafloor is dominated by an impressive circular volcanic caldera named Volcano “O”. Backscatter data acquired during our bathymetric surveys showed that Volcano O is the source of several lava flows covering large areas of the seafloor. Our plume surveys showed that Volcano O is also host to several active hydrothermal vents.

When we embarked on this expedition, we expected that we would be locating sites of steady hot spring activity, not areas affected by seafloor eruptions. Not only did we find indications of eruptive activity at one site on the NELSC, during that latter part of the expedition we encountered a second actively erupting site on the summit of a volcanic cone. As described in our Nov. 25 blog entry, a CTD cast over the summit of West Mata volcano encountered thick particle plumes with excess temperature up to 2 deg C and high concentrations of hydrogen gas. Although the West Mata plumes were close to the volcano summit, they had all the characteristics normally associated with active lava flows. Thus it appears that we found two regions of seafloor eruptive activity during our expedition.

Now all that remains is to pack up our gear and our samples, ship them back to our respective laboratories in Seattle and Newport, and begin additional measurements on these samples. These shore-based measurements should allow us to draw more definite conclusions concerning the origin of the diverse water-column plumes we encountered on this expedition.

Tuesday, Nov. 25

Map of West and East Mata Volcanoes

Marv Lilley
November 25

One of the things we do aboard ship to help understand the systems we are studying is to measure the concentrations of hydrogen and methane dissolved in the plume water samples we collect. These two gases typically have different origins in sea-floor hydrothermal systems. Hydrogen is produced by reactions between the host rock and hot seawater. Usually the hotter the water and the deeper the reaction occurs, the more hydrogen produced. Methane, on the other hand, is usually low in hot hydrothermal fluids and higher in low temperature fluids where it is produced by microorganisms.

On this cruise, we have seen a huge variation in the concentrations of these two gases. Early in the cruise we saw very high concentrations of hydrogen above the North East Lau Spreading Center (NELSC) which indicated that it was either erupting at the moment or had erupted in the very recent past. Most recently, we have been investigating two small volcanoes (East Mata and West Mata), which have very different concentrations of these gases. West Mata has about three times as much hydrogen in the plume water as we saw over the NELSC and is the world record for those of us aboard the Thompson. East Mata, on the other hand, has almost undetectable hydrogen but high concentrations of methane. Our tentative conclusion is that these two small volcanoes, which are only seven kilometers apart, are in different stages of their eruptive cycles with West Mata having erupted very recently.

Friday, Nov. 21

CTD plume hunters at work

l to r: John Lupton, Nick Dyriw, Jelena Puzic,

Ed Baker, Marv Lilley, Joe Resing

November 21, 2008

Ed Baker

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”?

Bathymetry of the area where a massive volcanic eruption is suspected

Tuesday, Nov.18

EM300 bathymetry at the Mangatolo triple junction,

collected aboard the R/V Thompson

November 18, 2008
Bob Embley

Susan Merle and I are on board to conduct the mapping operations with the EM300 multibeam sonar mounted on the T. G. Thompson’s hull. The system maps the seafloor in a swath about 4 miles across. The data collected with this system is processed on board providing a map of seafloor depth with a resolution of about 30 meters, roughly the size of a football field. These maps are then used to choose paths for the CTD tows in our exploration of the hydrothermal systems in the northern Lau basin. Our job is to provide geologic context for the optimal tow paths. An example of the data shows one of the more spectacular features of the area – a “triple junction” of three volcanic rifts. This type of feature is thought to be produced as the seafloor “swells” into a large dome from intrusion of magma and then cracks into three rifts as it fails under tension. We are in the process of finishing our survey of the Mangatolou Triple Junction before we move on to other areas further east. To date we have towed the CTD through the southern and western arms. The hydrothermal activity found to date is at the actual triple junction where the three rifts intersect.

Interpreting the seafloor geology “on the fly” using these spectacular maps is exciting and enjoyable but for me the hallmark of these types of expeditions is working with my colleagues on board to provide the most thoughtful and thorough exploration of this unique and virtually unknown part of the seafloor. Even after 42 years of going sea I continue to be awed at how little we really know about the 70 % of our planet covered by the oceans.

Susan Merle in front of the EM300 mapping console

Joe Resing and Gwen Hemery preparing the CTD for deployment

Friday, Nov. 14

The R/V Thompson at Apia Harbor (center), Samoa

Friday, Nov. 14
John Lupton, Chief Scientist

After testing the CTD/rosette system, we completed a single vertical water-column cast at about 15.0ºS, 173.1ºW en route to our study area. The location of this cast is a site where we have previously seen evidence of a regional helium plume, and therefore we wanted to sample it again. We are now in the process of generating a more detailed bathymetric map of the Mangatolo Triple Junction (MTJ) spreading center with the ship’s EM300 multibeam system. Next on the agenda is to tow-yo the CTD/rosette package back up the MTJ from south to north looking for evidence of hydrothermal plumes along the spreading axis.

On Tuesday previous to our departure, we benefited from the presence of a huge cruise ship that docked in Apia, Samoa. In order to make room for the cruise ship, the R/V Thompson was forced to leave the harbor for the day. This forced us scientists to take the day off and tour part of the island of Upolu. A group of about a dozen of us rented two vehicles and also paid for the services of an extremely entertaining Samoan tour guide named Sam. He drove one of the vehicles and gave us a non-stop commentary on local culture, sites of interest, etc. We had two opportunities to go swimming. The first was in a fresh water pool in a lava tube right by the ocean, the second was snorkeling over coral heads and colorful reef fish at a beach on Upolu’s south shore. But for many of us the highlight of the tour was Sam’s demonstration of how to open a coconut and make coconut cream. On Wednesday we were all back to work setting up our science equipment on the Thompson.

A beautiful beach on southern Upolu Island, Samoa

Sam making coconut cream

Vents Program Lau Basin 2008

Vents Program
R/V Thompson
November 2008

Expedition to search for hydrothermal activity in the NE Lau region by conducting water-column plume surveys. In conjunction with the water column work, expedition will also be doing bathymetric mapping of the seafloor using the shipboard EM300 system in areas where high resolution maps do not exist. The primary targets are the NE Lau Spreading Center (NELSC) , the Mangatolo Triple Junction (MTJ, also called the Kings Triple Junction), and the large caldera named Volcano O (Caldera on map).