A team led by a University of Houston professor reports the volcano, dubbed the Tamu Massif, is nearly as big as the giant volcanoes of Mars, placing it among the largest in the Solar System.
Located about 1,000 miles east of Japan, Tamu Massif is part of an underwater mountain range formed 130 to 145 million years ago by the eruption of several underwater volcanoes.
It had been unclear whether Tamu Massif was a single volcano, or a composite of many eruption points, but the researchers say they've confirmed the mass of basalt that constitutes Tamu Massif did indeed erupt from a single source near the center.
"Tamu Massif is the biggest single shield volcano ever discovered on Earth," Houston earth and atmospheric science Professor William Sager, the leader of the study, said. "There may be larger volcanoes, because there are bigger igneous features out there such as the Ontong Java Plateau, but we don't know if these features are one volcano or complexes of volcanoes."
Unlike most seafloor volcanoes, which are small and steep, Tamu Massif is low and broad, meaning the erupted lava flows must have traveled long distances, Sager said.
Tamu Massif covers an area of about 120,000 square miles.
"It's not high, but very wide, so the flank slopes are very gradual," Sager said. "In fact, if you were standing on its flank, you would have trouble telling which way is downhill.
"We know that it is a single immense volcano constructed from massive lava flows that emanated from the center of the volcano to form a broad, shield-like shape."
To find another volcano as large, the researchers said, one must look to the planet Mars, home to Olympus Mons, a giant volcano only about 25 percent larger by volume than Tamu Massif.