

Is This Undersea Monster Really the World's Largest Volcano?

Scientists announced last week that they'd found the world's largest volcano. But with their discovery buried beneath the ocean, how do we know for sure?
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The announcement last week set off a flurry of news reports with headlines such as "Underwater volcano is Earth's biggest" and "The Largest Volcano in the World Is Also the Shyest." Almost as quickly, though, came cautious words from the geoscience community, saying that a lot more data was needed before the newly discovered Tamu Massif volcano, buried deep under the Pacific Ocean, could lay claim to the title of largest volcano in the world, much less be a contender for the largest in our solar system.

"The issue with this work is that it's the first cut," Oregon State University volcanologist Shan de Silva says. "People discover something and they put it out there, and it really hasn't been scrutinized by the community. Yes, it's a big mass of stuff, but how long did it take to build that mass?"

Big doesn't really do justice to the sheer size of Tamu Massif. In the Nature Geoscience study announcing the find, the authors described the area as "immense" and "enormous." It measures 450 kilometers by 650 kilometers, covering an area of 310,000 square kilometers. That's larger than the United Kingdom and about the same size as Mars' Olympus Mons, widely considered to be the largest volcano in the solar system.

So what exactly is required to decree that Tamu Massif, a New Mexico–size portion of the Shatsky plateau, is, in fact, the biggest volcano in the world? It's not as simple as sending out some folks from Guinness World Records with a tape measure.

Geophysicist William Sager, who authored the study, spent years gathering data. He and his team collected rock cores, drilling into the area from a ship perched above the site. They also studied the echoes of sound waves, looking for the shape of the lava flows that built the massive rise.

Based on those data, Sager saw indications that Tamu Massif had formed quickly, from a single, central source of magma. But other geoscientists—including de Silva—say there could be other explanations for the formation. It could have formed from many different sources over a longer period of time, making it a really large, closely packed area of volcanoes but not the largest single volcano on earth.

There will be plenty to scrutinize in the next few years. Sager and his students are still analyzing the wealth of data they've collected from the seafloor and plan to continue to publish on the subject as their research progresses. Unfortunately, collecting more data is out of the question for now. Studying this far-flung area creates a particular set of challenges.


Scale is a huge problem when it comes to determining the size of this volcano. Simply, how do you get a handle on something so huge that's buried at the bottom of the sea? When discussing the drill cores collected from Tamu Massif by the scientists, Sager was quick to note that they'd "only" drilled about two-football-fields deep into the plateau, a pinprick compared with the 4-km height of the volcano itself—and that 4-km rise is only the part of the volcano that extends above the seafloor. Sager estimates that the root of Tamu Massif might be as deep as 30 km into the earth's crust, a depth that is impossible to sample directly with today's technology.

Sager and his team analyzed drill cores from three sites on Tamu Massif and did four cruises across the area to look at the layers of rock that formed the plateau. Those four trips used seismic technology, sending out bursts of sound and mapping the echo of the seismic waves as they bounced back off the layers of rock under the surface.

But all that work was spread over a huge area. Sager compares it with driving along four highways in New Mexico and coming to a conclusion about the geology of the state based on those four trips. "That's the life of a marine geophysicist," Sager says. "I would love another couple or three months out there."

Out to Sea

Studying the seafloor is a difficult proposition in the best of times, made more difficult by the vagaries of weather and equipment and the barrier of many kilometers of water between the scientists on the ocean surface and the formations they're studying. Getting to the location is no picnic, either. The Shatsky Rise where the Tamu Massif is located is a four-day boat trip from Japan and 10 days from Hawaii.

Sager and de Silva compare studying the geology of the ocean floor to studying the geology of other planets. "The fact that we've only just discovered this thing, but we've known about Olympus Mons for the past 40 years tells you something," de Silva says.


Based on samples gathered from the drill cores, Sager determined that the volcano is roughly 144 million years old, dating back to the time of the dinosaurs. The area could have formed relatively quickly over the course of 1 to 2 million years, or it could have taken much longer. Without more samples and direct dating of the layers of the structure, it's hard to say definitively whether this was a single volcano or many overlapping volcanoes from different sources.

If it does prove to be a single volcano, it could have major implications for how geologists look at the formation of oceanic plateaus, which were long thought to have come from multiple sources of magma.


"This is exciting and interesting work, but it is early days," de Silva says, calling for more detailed scrutiny of the claims.

Why not go back and get more data to prove that this is absolutely, positively the biggest volcano yet discovered on earth? There's just not enough money. Going out on a research cruise to drill cores of rock from the seafloor or send booming seismic waves down into the earth's crust to image the area costs a lot of money. Sager says that the cruises to drill for samples or gather seismic profiles can cost millions of dollars each, and research budgets are tight.

While research dollars could go toward additional cruises out over Tamu Massif, the fact is there are also plenty of other areas just waiting to be explored. Tamu Massif is just one of several oceanic plateaus of a similar size and shape lurking under the sea.

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