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.