Massive Underwater Shield Volcano Rivals the Largest in the Solar System
The summer blockbuster movie Pacific Rim told a fanciful tale of giant monsters rising from the deep in the middle of the Pacific Ocean. Now, scientists have confirmed that the northwest Pacific is home to a real-life giant of a different type: the largest single volcano yet documented on Earth. Covering an area roughly equivalent to the state of New Mexico, 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 the largest feature of Shatsky Rise, an underwater volcanic mountain range formed 145-130 million years ago. Until now, it was unclear whether Tamu Massif was a single volcano, or a composite of many eruption points. By integrating several sources of evidence, including core samples and data collected on board the JOIDES Resolution, the authors have confirmed that Tamu Massif erupted from a single source near the center. The study appears in the September 8 issue of Nature Geoscience.
“Tamu Massif is the biggest single shield volcano ever discovered on Earth,” says lead author Will Sager at the University of Houston. “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.”
The seafloor is dotted with thousands of underwater volcanoes, or seamounts, most of which are small and steep. Among these, Tamu Massif stands out not just for its size, but also its shape. It is low and broad, meaning that the erupted lava flows must have traveled long distances compared to most other volcanoes on Earth.
“The flank slopes are very gradual,” Sager explains. “In fact, if you were standing on its flank, you would have trouble telling which way is downhill. Oceanic plateaus are huge features hidden beneath the sea. They have found a good place to hide.”
Tamu Massif covers an area of about 120,000 square miles. By comparison, Hawaii’s Mauna Loa – the largest active volcano on Earth – is about 2,000 square miles, or less than 2% the area of Tamu Massif. To find a worthy comparison, one must look skyward to the planet Mars, home to Olympus Mons. That giant volcano, which is visible on a clear night with a good backyard telescope, is only about 25% larger by volume than Tamu Massif.
The study relies on core samples collected on Integrated Ocean Drilling Program (IODP) Expedition 324 (Shatsky Rise Formation) in 2009, and seismic reflection data gathered on two expeditions of the R/V Marcus G. Langseth in 2010 and 2012. The core samples showed that Tamu Massif is made of lava flows up to 75 feet thick. Seismic data from the R/V Langseth cruises revealed the structure of the volcano, confirming that the lava flows emanated from its summit and flowed hundreds of miles downhill.
“Other scientists care about this finding because it gives us new insights about oceanic volcanism, the way in which oceanic plateaus form, and the operation of the mantle-crust system,” Sager explains. “Volcanologists debate about the eruptive centers of Large Igneous Provinces. I think most would tell you that they probably come from multiple, distributed fissure eruptions. But apparently not at Tamu Massif.”
