The world's largest volcano lurks beneath the Pacific Ocean, researchers announced today (Sept. 5) in the journal Nature Geoscience.
Called the Tamu Massif, the enormous mound dwarfs the previous record holder, Hawaii's Mauna Loa, and is only 25 percent smaller than Olympus Mons on Mars, the biggest volcano in Earth's solar system, said William Sager, lead study author and a geologist at the University of Houston.
"We think this is a class of volcano that hasn't been recognized before," Sager said. "The slopes are very shallow. If you were standing on this thing, you would have a difficult time telling which way was downhill."
Tamu is 400 miles (650 kilometers) wide but only about 2.5 miles (4 km) tall. It erupted for a few million years during the early Cretaceous period, about 144 million years ago, and has been extinct since then, the researchers report.
Like other massive volcanoes, Tamu Massif seems to have a central cone that spewed lava down its broad, gentle slopes. The evidence comes from seismic surveys and lava samples painstakingly collected over several years of surveys by research ships. The seismic waves show lava flows dipping away from the summit of the volcano. There appears to be a series of calderas at the summit, similar in shape to the elongated and merged craters atop Mauna Loa, Sager said.
Until now, geologists thought Tamu Massif was simply part of an oceanic plateau called Shatsky Rise in the northwest Pacific Ocean. Oceanic plateaus are massive piles of lava whose origins are still a matter of active scientific debate. Some researchers think plumes of magma from deep in the mantle punch through the crust, flooding the surface with lava. Others suggest pre-existing weaknesses in the crust, such as tectonic-plate boundaries, provide passageways for magma from the mantle, the layer beneath the crust. Shatsky Rise formed atop a triple junction, where three plates pulled apart.