27 April 1999

Active Submarine Volcano Found Near Samoa

Researchers have discovered an active volcano on the ocean floor in the Samoan islands. The volcano rises some 4,300 meters (about 14,000 feet), is more than 35 kilometers (about 22 miles) across at its base, and peaks at just 600 meters (2,200 feet) below the surface of the water. Its peak is marked by a circular caldera some two kilometers (about one mile) across and 400 meters (1,300 feet) deep. A team of National Science Foundation funded researchers made the discovery, which contributes greatly to the scientific debate over the formation of hot spot island chains.

Given that the discovery was made in an area that was considered to be well surveyed, the find "underscores just how little we know about the ocean floor" according to Dave Epp, program director in NSF's division of ocean sciences. The new volcano was discovered by a team lead by Stan Hart, a geochemist at the Woods Hole Oceanographic Institution. The location had been predicted based on a 1995 earthquake swarm in the region. The volcano has been named Fa'afafine, roughly translated from the Samoan meaning 'wolf in sheep's clothing', a name that seemed appropriate name since the size and location of the volcano was a surprise, according to Hart.

The existing seafloor maps of 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 only showed a small hill-like geologic feature, one of many unnamed features in the island chain. Hart decided to look closer at several of the features. A detailed survey with the research vessel Melville 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 contend. The classic example of a hot spot island chain is the Hawaiian Islands, where what will one day 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 slowly migrates 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 are 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.