April 16, 1999
An active volcano rising more than 4,300 meters (over 14,100 feet) from the ocean floor in the Samoa Islands has been discovered by a team of U.S. scientists, providing more evidence to the scientific debate over the formation of hot spot island chains. The volcano, more than 35 kilometers (about 22 miles) across at its base, rises to within 600 meters (about 2,000 feet) of the surface; its peak is marked by a circular caldera some two kilometers (over 1 mile) across and 400 meters (1,300 feet) deep. It is similar in size to Mt. Whitney in California, the largest mountain in the contiguous 48 U.S. states.
The new volcano was discovered by Stan Hart, a geochemist at the Woods Hole Oceanographic Institution and chief scientist on the recent cruise, and his colleagues in March. The location had been predicted based on a 1995 earthquake swarm in the region. The volcano has been named Fa’afafine, a Samoan word that very loosely translated means wolf in sheep’s clothing. “It seemed an appropriate name since the size of the volcano was a surprise and wasn’t at all what it appeared to be,” Hart says. “The available ocean floor bathymetric maps of the area gave us no indication of what is really there on the ocean floor. It’s very exciting to find a feature this large more or less where predicted.”
The existing maps of the seafloor in the area, made by satellite altimetry a few years ago and considered the most accurate maps available, gave little indication of the actual size of the volcano. They simply showed a small hill-like geologic feature, one of many unnamed features in the island chain. Hart, whose research focuses on the formation of the earth’s mantle and the evolution of hot spots, decided to look closer at several of the features. A detailed survey with the research vessel using Sea Beam multibeam sonar revealed the true size of the volcano, and the stunning perfection of the summit caldera, along with the first detailed information about other features on the ocean floor around several of the nearby islands.
Hart and his colleagues went to the area to test the idea that the Samoa Islands are a volcanic hot spot chain, and to prove that their formation is not principally related to proximity to the nearby Tonga Trench, as some earth scientists believe. The classic example of a hot spot island chain is the Hawaiian Islands, where what will someday be the newest island, Loihi, is a seamount rising toward the ocean surface on the southeast flank of the island of Hawaii. These volcanic chains are formed as the Pacific lithospheric plate migrates slowly northwest over a hot upwelling of the underlying mantle. Hart believes that the Samoa Islands chain, like the Hawaiian Islands, is indeed such a hot spot chain, with the youngest volcano at the end of the chain. Fa’afafine, at the far eastern end of the Samoa Island chain, likely represents the present location of the “hotspot”.
Hart and his colleagues collected tons of rock samples in 17 dredges at various target sites in the area. Three of the dredges were collected in the caldera of Fa’afafine and three more on the outside rift zones of the seamount. Seismic records reveal a 1995 earthquake swarm in the vicinity, and Hart says that the earthquakes may be directly linked to the eruption of the volcano. The very fresh appearance of many of the dredged rocks from the caldera provide clear evidence of a young or recent eruption.
Other scientists on the cruise with Hart were Hubert Staudigel of the Scripps Institution of Oceanography, Mark Kurz of the Woods Hole Oceanographic Institution (WHOI), and Alberto Saal, a graduate student advised by Hart at WHOI. Erik Hauri of the Carnegie Institution of Washington, formerly a graduate student at WHOI, was unable to make the cruise but will take part in the geochemical analyses of the rocks. The week-long cruise was conducted aboard the Research Vessel Melville, operated by the Scripps Institution of Oceanography, and was funded by the National Science Foundation.
Hart and his colleagues are already planning a return trip to the volcano, and are hoping to use a remotely operated vehicle or human occupied submersible to survey the caldera in detail, and to search for hydrothermal hot springs and associated biota. In the meantime, the team is anxious to begin analyzing the nearly 300 pounds of rocks which they hand-carried back to Woods Hole. The remaining several tons of rock samples will arrive sometime in June when the Research Vessel Melville returns to Hawaii and the samples are off-loaded and shipped to the researchers.