Final 2010 expedition posting: Tofa Soifua

Tofa Soifua and Goodbye from Samoa and the Kilo Moana

Joe Resing Chief Scientist

The science party

Monday May 10th, 2010. We are currently sitting outside of Apia, Western Samoa, waiting to return to shore. It is sunrise and another beautiful day in paradise. We made remarkable discoveries on this voyage and accomplished much of what we set out to do. Although the ship has been beleaguered by a host of problems and we have had to return early, it was through the hard work and dedicated effort of the crew of the R/V Kilo Moana that we were able to accomplish so much.

The NE Lau basin is an area of intense magmatic and volcanic activity. It always seems that the next hydrocast will reveal yet another volcanic eruption or site of intense hydrothermal activity. On this trip we concentrated a lot of our effort on the North Mata volcanoes. Our findings indicate that 6 of those 7 volcanoes are active. Including our previous findings of magmatic and hydrothermal activity at East and West Mata, we have found activity at 8 of the 9 Mata volcanoes. These volcanoes form a chain only 15 -16 nautical miles long making this one of the most intense areas of hydrothermal activity found on Earth. Why is this? This area of the seafloor appears to be opening and cracking, allowing more magmatic activity, making these volcanoes very different from those that we find along the mid-ocean ridge, back arc spreading centers, and even those found along the arcs.

We also found that these sites support much biological activity. This is important, because the northern-most Mata volcano represents a biogeographic terminus of hydrothermal activity for this region. In order for species to spread, there is a large geographic barrier that they must now cross to propagate to and colonize in other areas of the oceans. Each of the northern Matas is venting very methane-rich hydrothermal fluids. Methane is an important source of microbial energy and is likely one of the important energy bases for the hydrothermal food chain found at these sites (see the rocks and animals blog posting).

Vent endemic fauna at one of the northern Mata volcanoes.

Crinoids cling to the top of a chimney-like structure on one of the northern Mata volcanoes.

We look forward to our eventual return with a deep-sea robotic vehicle so that we may fully study this very exciting and incomparable place in the world’s oceans. Although we overuse the word unique, as of now we have found no other place on earth that is like the place we have found on this voyage.

Acoustic Glider

Listening to the Seafloor from Afar

Acoustic Glider Team

The glider in the water soon after deployment.

Scientists and engineers from NOAA/ Pacific Marine Environmental Laboratory’s Vents Program successfully flew an ocean glider for hunting underwater volcanic plumes and eruptions in the Northern Lau Basin in the South Pacific near Samoa and Fiji. The team of scientists and ship's complement on the R/V Kilo Moana deployed and recovered the glider while 5000 miles away a team of engineers on shore controlled the glider 24 hours a day during this two-day mission. The ocean glider “flys” by controlling its buoyancy with respect to surrounding seawater and repeating dives and ascents between the surface and 950 meter depths at 3-3.5 hour intervals. The ocean glider can go up and down in the water column by use of a pump pushing oil in and out of its internal oil reservoir to an external bladder in the nose cone and converting the resulting vertical motion to horizontal momentum through its wings. During each surfacing, the glider calls in via satellite to a shore side team and transmits data from its latest dive and ascent. The lack of a physical propulsion system allows for “quiet” operation of the glider, enabling high quality sound recordings of nearby erupting volcanic vents. In addition to the hydrophone used for recording volcano sounds, the glider is equipped with instruments able to detect temperature, conductivity and turbidity anomalies associated with hydrothermal and eruptive plumes.

The glider path from launch to recovery.
The yellow points are the positions when the glider surfaced.

The glider performed flawlessly during the mission. Ironically the only problems arose because of the delicate nature of the technology and communications issues. A two day window of calm seas was critical because the glider had to be recovered carefully by small boat and towed carefully over to the ship and hooked onto a lifting line. Choosing the launch time required constant coordination between the shore and ocean teams over a week period. Also, during the pre-dive diagnostics prior to deployment of the glider, satellite communication between the glider and the PMEL shore station was less than ideal and attributed to interference from the steel structure of the ship. However, once deployed in the water, we experienced very few satellite communication issues. The Kilo Moana’s e-mail service was excellent and helped tremendously in coordinating the operations between the ship and shore teams.

Recovering the glider using the ship's Zodiac.

During this mission, engineers at PMEL in Seattle and Newport worked together to monitor the progress of the glider and report its position and status to ship board personnel around the clock. Over the two-day mission, the glider travelled roughly 50km from the Northeast Lau Spreading Center (NELSC) to the volcanic cone at West Mata where it was met by the ship and recovered. Despite working upstream against a surface current of 30-40cm/sec, the glider made good forward progress averaging 30cm/sec headway toward its waypoints. The glider’s navigation was amazingly accurate during a nearly flawless flight. Currently, data from the mission are being analyzed and we expect that it will reveal new insight of the plumes near the West Mata area as well as the acoustic signature unique to active seafloor volcanism.

Mapping

Mapping the Northeast Lau Basin

Susan Merle

3-D image of the NE Lau Basin seafloor. Bathymetry data were collected during expeditions to the area is 2008, 2009 and on the present mission. Data are 2 times vertically exaggerated.

The main objective of this expedition has been to further our understanding of the extensive volcanic activity in the northeast Lau Basin. We wouldn’t know where to look if we didn’t have a good map of the seafloor. Seafloor mapping was performed between TowCam and CTD operations on this mission. Some areas were mapped to fill gaps in our data coverage, others were mapped to perform surface differencing calculations which tell us where new lava has erupted or landslides have occurred. The bathymetry data are gridded and can be displayed as a 2-D map, a 3-D image, or utilized interactively as a layer in a GIS (Geographic Information System) database.

The mapping system is mounted on the hull of the R/V Kilo Moana. A sound signal called a ping is sent from the ship to the seafloor and bounces back to the ship. The length of time that it takes for that round trip is how the seafloor depth is determined. Over the years seafloor mapping systems have improved immensely. During the 1980s the NOAA Vents Program mapped the Juan de Fuca ridge with the first generation of seafloor mapping systems called SeaBeam classic. That system had 16 soundings, called beams, on each ping. Coverage was 75% of the water depth, eg. if the water was 1000 meters deep the swath on the bottom was 750 meters across. The new EM122 12 kHz multibeam system on the R/V Kilo Moana has a possible 432 beams per ping. The coverage averages 4 times water depth (4000 meters across in 1000 meters of water). The resolution of the data has increased dramatically due to the increase in data density. The EM122 is a new generation of multibeam system, capable of mapping the water column as well as the seafloor. The water column data images biomass (fish, zooplankton, etc.) as well as bubble plumes rising from the seafloor. On our past expedition to the Mariana Arc we successfully imaged gas bubble plumes rising from the eruptive vents at the summit of NW Rota volcano (http://nwrota2010.blogspot.com/2010/03/volcano-mapping.html).

On this expedition we departed from the island of Upolu Samoa, steamed southwest crossing the Tonga Trench to the Lau Basin – mapping all the way. Mapped depths range from 150 meters near the island to 7200 meters over the trench. Approximately 4000 square kilometers of seafloor was mapped in the expedition operations area where water depths range from 1000 to 3800 meters.

Bathymetry data collected on the 2010 expedition are outlined in black.

More Smoking Guns

More Smoking Guns in the Lau Basin

Ed Baker and Bob Embley

Elemental sulfur deposits on the summit of the central cone at Volcano O.

A scientist is simply another version of a detective, endlessly seeking clues to how the world works. Here in the Lau Basin, one of the most geologically active patches of ocean floor on the planet, our forensic tools are several varieties of remote sensing instruments. Our assignment is to discover where molten magma from the Earth’s mantle rises close enough to the seafloor to create hot springs in the icy depths. These hot springs, similar to those at Yellowstone National Park, are oases for isolated ecosystems that can survive only on the heat and chemicals venting from the seafloor.

Last year in the Lau Basin, we reported the discovery of one of the most remarkable hot spring environments ever discovered (see our 2009 blog entry on the right side of this page). Video from the West Mata volcano summit showed erupting molten lava and exploding magma gas bubbles. This year we are again uncovering more evidence of spectacular hot spring activity in this seafloor wonderland.

We have finished examining the “Northern Matas” volcano group (see the May 5th Synopsis) and have confirmed that active hot springs occur on six of those seven volcanoes. Thus eight of the nine “Mata” volcanoes in this corner of the Lau Basin host active hydrothermal fields. Discovering so many active volcanoes in such a confined area is unprecedented in our experience. But our most stunning discovery was not in this area but several miles to the southwest, at Volcano “O”, one of the largest volcanic calderas ever mapped on the deep sea floor.

Map of Volcano "O"

Rising a thousand feet from the southeast corner of the caldera floor is a perfectly symmetrical volcanic cone. This edifice is probably the youngest volcanic feature on Volcano O, constructed of lavas and fragmental material to form an almost perfectly symmetrical volcano rising up 300 meters (~1000 feet) from the floor of the caldera. We dropped a CTD cast directly on its top and recorded hydrothermal plumes as intense as those enveloping the summit of West Mata—a literal smoking gun. The similarity to West Mata energized us to conduct a camera tow directly over the summit of the cone. This operation was a delicate one as the cone narrows upwards to a very small pinnacle. The camera group (see the May 3 blog) was up to the job, of course, and the camera climbed up the steep (≥ 30°) northwest flank and passed directly over the top.

Real-time sensors on the camera frame reported tantalizing data. Along its path across the summit it encountered dense particle plumes, high oxidation-reduction anomalies (indicating an increased concentration of chemicals like hydrogen sulfide that are vital for seafloor microbial life), and higher temperatures. Clearly the top of cone was the muzzle of a smoking gun. It was agonizing waiting until the end of the tow to see images of the seafloor itself.

The images were well worth the wait! The flank of the volcano consisted of long
toothpaste-like lava flows, black sand, and lighter colored sediment.

The seafloor along the flanks of the central cone at Volcano O.

But as we neared the summit, patchy white reflective material became more and more common until almost the entire slope was covered. Finally, near the southern edge of the summit, we encountered drifting clouds of milky white fluid that appeared to be seeping out of the seafloor over a broad area.

A close look at the photographs showed that the clouds were high concentrations of dense white particles. The white patches we saw scattered around the summit must be deposits of these same particles. Evidence from the water samples collected on the CTD cast, and from the TowCam photos, suggest that the specks are elemental sulfur. In fact, the scene at the summit of the cone is reminiscent of Daikoku volcano in the Mariana arc where in 2006 we discovered an extraordinary pool of liquid sulfur bubbling on the seafloor (http://oceanexplorer.noaa.gov/explorations/06fire/logs/may4/may4.html). Beyond these exciting inferences, we won't know what new discoveries await us at Volcano O until we return with a robotic vehicle (ROV) on a future cruise. Our case in the Lau Basin is far from being closed, and many more clues are left to be revealed.

Rocks and Animals

Rocks and Animals on the Seabed in the NE Lau Basin

Ken Rubin

One of the activities on this expedition is systematic high-resolution photographic surveys of the sea floor. Why do we want to do that? To learn what is there. After all, the deep sea floor is Earth’s final frontier and we are driven to explore it. But why go to the NE Lau basin, instead of some place closer to home? We already know that many areas on the sea floor are vast monotonous plains of sediments, and that other parts are as rich with features as the land above sea level. The NE Lau basin is one of those feature-rich places. Sonar maps tell us that it has a larger than usual number of hills, ridges, basins and cracks that are characteristic of volcanic landscapes. Chemical surveys of the overlying sea water tell us that some number of these hills is hydrothermally active. So, we’ve come to this area to learn which areas have young volcanic rocks, hydrothermal mineral deposits and/or animals that thrive at active volcanoes.

Large brown gastropods colonize hydrothermal chimney structures on one of the volcanoes of the North Mata group. As Tim Shank (a colleague at Woods Hole Oceanographic Institution) explains, these seamounts may have faunal differences between them that are related to geography, the age of the venting system, recent disturbances, or some combination thereof.

By photographing the sea floor, we can see first hand what types of rocks are there, what condition they are in, and what organisms might be living on them. We have chosen our survey spots mostly from sonar maps and sea water chemical data. But we also use a bit of horse sense and rely on a bit of luck to hopefully put the camera down in the best spots. So far, we have completed 7 camera surveys, and our luck has been with us. We have discovered relatively young (less than a century or so old) volcanic rocks at each site, and active hydrothermal systems at two of them.

Young, fresh pillow lava in a newly discovered lava flow erupted near Tafu volcano on the NE Lau Spreading Center. The white deposits on the surfaces of the cracks usually only lasts for a few years after eruption.

Young sheet lava overlies fresh pillow lava, showing a sequence of lava effusion conditions (slower at first, and then faster) at this spot during the eruption near Tafu.

These photos also provide invaluable first hand information about the types and numbers of animals that live these at submarine volcanic sites. The animals tell us where nutrient and energy rich hydrothermal fluids are venting from the rocks (which is sometimes difficult to see with the naked eye). But more importantly, they inform us about the ecological conditions that allow some of Earth’s most unusual critters to grow, reproduce, migrate and colonize the isolated spots in the deep sea they are adapted to live in. So far, we have discovered two sites that are rich in such fauna on this expedition and by harnessing the R/V Kilo Moana’s reliable and speedy Internet link to send photos to shore, we have been able to learn a great deal about these communities. Dr. Tim Shank, a colleague at Woods Hole Oceanographic Institution, who was unable to come with us on the expedition, tells us that these sites are rich in fauna, some found elsewhere in the region, and some that might be new discoveries. Some notable examples are included in the last two pictures on this page.

Crabs, Phymorhychus gastropods (large white snails) and small actinarian anemones populate a volcanic substrate with active diffuse hydrothermal venting. None of the species, or those in the first picture on this page, were found at actively erupting West Mata volcano during our remotely operated vehicle dives in 2009.

TowCam - The Right Tool

TowCam – the Right Tool for the Job Exploring the NE Lau Basin

Bob Embley

The state-of-the-art maps we make using the R/V Kilo Moana’s hull-mounted sonar systems provide us with a great view of the major seafloor features such as volcanoes and fault zones. However, even the best maps of the seafloor require interpretation that is limited by the resolution of the map (the maps we have out here have data points about every 25 meters (~85 feet). Although we can make basic interpretations using these maps such as the presence of hard rock and the type of seafloor landforms, we still have to have images of the seafloor to make finer observations such as composition of the seafloor and the seafloor biological communities. Robotic vehicles and human occupied submersibles are being increasingly used to provide this need but they are expensive and difficult to deploy on short notice. Another lower tech yet very effective way to image larger areas of the seafloor is the deep-towed camera.

Preparing the TowCam for deployment from the stern of the R/V Kilo Moana (left to right: Justin Smith, Susan Hannemann, Ken Feldman). The large fin stabilizes the fish during towing. Orange objects are batteries used to power the digital camera strobe.

The “TowCam” we are using is one of several designed and built at Woods Hole Oceanographic Institution by D. Fornari and M. Schwartz for use by the scientific community. It has evolved from earlier systems developed in the 1960s and 1970s to locate hydrothermal vents and to photographically map the seafloor. The well-designed TowCam includes a digital camera, a light strobe, a sonar designed to monitor the height of the sled off bottom which provides warning of steep topography along its path, a pressure gauge to record depth, and various other sensors to precisely measure temperature, water turbidity etc. The “TowCam” also has six bottles that sample water over hydrothermal vent fields. These instruments are all mounted within a sturdy frame to protect them from accidental contact with the seafloor. The entire system is connected to one of the ship’s deep-sea cables and lowered to about 15 feet off the seafloor where it is towed at slow speed (1/4 knot) over features of interest. The slow tow speed is critical for maintaining maximum control of the camera and ensuring a high spatial density of photographs. On this expedition we have been collecting 2000 high resolution photographs, snapped every 10 seconds over a tow path of about 2 miles.

TowCam photograph of coral hanging on for dear life on unstable volcanic slope of Mata Fitu volcano. Depth approximately 2440 meters (~8000 ft.). Two green dots just above coral are lasers with separation of 15 centimeters (~6 inches).

The progress of the camera is monitored by the scientists on the ship. On this trip we are dependent on the technical expertise of Ken Feldman who has not only kept the system operational but is a master at “flying” the camera near the seafloor using the ship’s winch. Susan Hanneman has volunteered her long expertise and enthusiastic support of the TowCam operation on this expedition and we are also dependent on the expertise of Susan Merle to provide the detailed seafloor maps of the camera tracks.

Scene in lab of Kilo Moana during TowCam operation. Front: Susan Hanneman (left) and Ken Rubin (right) Back: Ken Feldman (left) Craig Harvey (right). Large monitor displays seafloor map of area being towed and control for winch is seen just to left of Ken Feldman.

May 5th Synopsis

We have now been at sea one week, already half-way through this expedition to the Lau Basin. During this first part of the cruise our main scientific objectives have been to search for new volcanic activity, as well as to verify whether or not volcanoes visited on past cruises are still active. Two methods of exploration have been used. The first is a suite of sensors on board a CTD-rosette sampler system that is lowered from the ship, which enables us to detect hydrothermal and volcanic activity on the seafloor. The second method is a camera sled that is towed near the seafloor, providing images of lava flows, biota, and hydrothermal vents.

Up to this point our operations area has been the Mata group of volcanoes. West Mata, the volcano that was erupting lava onto the seafloor during our last visit in 2009 is still extremely active (see our blog entries from the 2009 expedition link on the right side of this page). The hydrothermal system at East Mata is also still emitting hydrothermal fluids. The main focus area has been the "North Matas", an area not previously explored by our group. CTD tows have been executed across all of the northern Matas and all but one have a hydrothermal signal. In addition 2 camera tows on the northern Matas reveal hydrothermal vent biota, as well as extinct and active sulfide chimneys.

Camera tow image of chimneys on one of the northern Matas.
The chimneys in this image don't appear to be emitting hydrothermal fluids.

Biota in the region of the previous chimney image.
Crab species, shrimp and urchins are present.

CTD towyo over one of the North Mata volcanoes.
Orange and red colors indicate high particle concentrations over the summit.

The NE Lau basin appears to be one of the most magmatically active place on earth. Our previous research shows evidence of extensive volcanism in the region. Many areas are covered with relatively young lava flows. So, in addition to looking at the Mata group of volcanoes, we also performed 4 camera tows over some of those lava flows. When magma is erupted on the seafloor and is cooled by hydrothermal activity, it releases a rare elemental tracer, helium (3He). A large helium anomaly exists throughout the region, the source of which is unknown. In an effort to better identify the source, three CTD vertical casts were acquired in the area of the Tonga trench. This long-term project is one we will continue to pursue.

At this point we have performed 14 CTD operations, 8 of those have been tow-yos and 6 have been vertical casts. 7 camera tows have been completed. Stay tuned.