Scientists Find Active Underwater Volcano East Of Samoa

Mapped and sampled last year for the first time, Stanley Hart of WHOI and Hubert Staudigel and Dave Willoughby of SIO returned in March of this year to search for evidence that the volcano is actively erupting. By towing an instrument behind the ship that measures the turbidity or particulate matter in the water column, the researchers were able to show that the summit crater of the volcano is filled with billowing "smoggy" water. This "smog" extends out from the top of the volcano, in the form of a halo, for more than five miles. Both the 1999 and 2000 cruises were funded by the National Science Foundation.

The scientists were working from the U.S.Coast Guard Icebreaker Polar Star, which was on its return trip from Antarctica after "summering" there since December. Helicopters from the ship picked up the scientists on Fiji March 19, and the ship arrived on top of the volcano the next day. The circular summit crater of Vailulu’u is 400 meters (about 1,300 feet) deep and 2,000 meters (about 6,500 feet) wide, and appears to be the location of the current volcanic activity.

The scientists first surveyed the water in and around Vailulu’u for turbidity, temperature and salinity using a "tow-yo" technique. While the ship steams slowly along a chosen track, the instrument package is continuously lowered and raised on the end of a cable, and the various readings are displayed on-deck in real time. The surveys indicated the "smog" outside the crater was restricted to a layer in the water between depths of 600 and 800 meters (about 1,950 to 2,600 feet deep), and is apparently being carried out of the crater and dispersed by ocean currents. Water samples were collected during the profiling, and these are being analyzed for chemical constituents that may shed light on the nature of the process forming the "smog."

The scientists also deployed five hydrophones, or underwater microphones, onto the upper reaches of the volcano, including the crater floor. These instruments will "listen" for and record earthquakes and other volcanic rumblings until they are retrieved next spring.

Hart and his colleagues say their finding of a dense smog layer justifies a return mission to Vailulu’u with a major exploration campaign utilizing submersibles and remotely operated vehicles (ROVs). Future work will involve searching the crater area for hot springs and possible associated biological communities, and mapping the lava flows as a means for understanding how such submarine volcanoes are constructed and how they grow to become ocean islands.

The origin of the Samoa island chain has long been debated among geochemists and other earth scientists. Some argue that the islands have followed a classic hot spot track, like the Hawaiian islands. Others argue instead that the origin is related to rifting or crustal plate activity associated with the northern terminus or end point of the Tonga Trench, based on the presence of active young volcanos along the chain from Savai’i to Ta’u. Harts says the discovery of Vailulu’u Volcano, well to the east of any possible influence from the Tonga Trench, and therefore the newest of the Samoan volcanoes, supports a hot spot model for the Samoan chain. "Just as Loihi is the newest volcano in the Hawaiian chain," he notes, "Vailulu’u is the Samoan equivalent of Loihi."

First discovered in 1975 by Rockne Johnson and named Rockne Volcano, this seamount was the site of a swarm of sizable earthquakes in January 1995, perhaps signaling the beginning of its current eruptive cycle. Prompted by this earthquake swarm, Hart and Staudigel mapped and sampled the seamount in March 1999. Unaware at the time of the 1975 discovery by Johnson, they informally named the seamount Fa’afafine Volcano.

The school children of American Samoa recently held a contest to pick a more lasting name. The winning entry, Vailulu’u, was submitted by Taulealo Vaofusi from Samoa High School, and announced during the 100th year Flag Day celebration on April 21, 2000. Vailulu’u is the sacred sprinkling of rain that reportedly always fell as a blessing just before a gathering of the great King Tuimanu’a, an icon of Samoan cultural life.

"Officially naming Vailulu’u at the 100th Flag Day celebration," Hart adds, "welcomed the, as yet unborn, newest island to the culturally rich Samoan archipelago."

##

Related Link: 3D Rendering of Vailulu'u Volcano: http://www-pacer.ucsd.edu/avon/samoanHS2.htm