Overview of the Volcano
Under the Pacific Ocean, some 1,000 miles (1,600 kilometers) east of Japan, a volcano the size of New Mexico or the British Isles have been discovered, making it the largest volcano on Earth and one of the largest in the solar system.
The massive shield volcano, known as Tamu Massif, was previously assumed to be a composite of smaller structures, but experts now say they must reconsider long-held assumptions about marine geology.
“We found that it’s one gigantic volcano, which goes against what we thought,” said William Sager, a geology professor at the University of Houston in Texas. Sager is the lead author of a report about the discovery that was published this week in Nature Geo-science, a peer-reviewed journal.
“It’s on par with Olympus Mons on Mars, which was once thought to be the solar system’s greatest volcano,” Sager told National Geographic.
The Tamu Massif is a Spherical Dome
Tamu Massif is a spherical dome that spans over 100,000 square miles and is 280 by 400 miles (450 by 650 kilometers). Its peak is around 6,500 feet (2,000 meters) below the water’s surface, and its base is nearly 4 miles (6.4 kilometers) deep. Tamu Massif dwarfs Mauna Loa, the world’s largest active volcano, which encompasses about 2,000 square miles and is located in Hawaii (5,200 square kilometers).
Tamu Massif, which is made of basalt, is the oldest and largest feature of the Shatsky Rise, an oceanic plateau in the northwest Pacific Ocean. In addition, the overall size of the rise is comparable to that of Japan or California.
Sager has been investigating the Tamu Massif for over 20 years. Tamu Massif was called after the scientist’s former workplace, Texas A&M University; massif is French for “huge” and is a scientific term for a large mountain.
Scientists had known about the Shatsky Rise since it was originally charted in the early twentieth century, he explained. “We knew it was a large mountain range, but we had no idea what the structure looked like or how it formed,” Sager explained.
Tamu Massif, he continued, is distinct from traditional seamounts, which are tens of thousands of volcanoes that protrude from the ocean floor around the planet. Tamu Massif is substantially larger and has a gentler slope than traditional seamounts, according to Sager.
Brief of the Underwater Volcano
The slope at the summit of Tamu Massif is only about one degree, he noted. The slope is half a degree down the flank, and it’s even less near the base. (A 40-degree stairwell has an average slope of 40 degrees, whereas a 10-degree easy ski slope has an average slope of 10 degrees.)
”It would be difficult to know which way is down if you were standing on the massif,” Sager remarked.
Identifying an Odd Structure
Scientists had assumed that the massive Shatsky Rise originated over time as a composite of multiple volcanoes that grew together, similar to how Hawaii’s huge island was produced by the eruptions of five different volcanoes in close vicinity.
When Sager and colleagues examined seismic data from the Tamu Massif, however, they were taken aback by what they discovered.
“We witnessed what appeared to be lava flows extending out in all directions from the core of the volcano, with no clear big secondary source of volcanism,” Sager added.
A geochemical study was also carried out on core samples collected from the massif. They discovered that the massive structure was built of the same rock and the same age.
As a result, the scientists concluded that Tamu Massif was formed by a single volcano during a very brief period of a few million years. Saged said that the volcano became “extinct,” or inactive, shortly after it formed. That happened some 145 million years ago, during the Late Jurassic to Early Cretaceous period.
Brian Jicha, a geologist at the University of Wisconsin who has received funding from National Geographic to examine the origin of the Aleutian Islands, stated, “If what they are claiming is right, that is truly a big volcano.”
“There are a lot of these oceanic plateaus, so if some of them are just volcanoes, this paper might begin to shift the way we think about how oceanic plateaus, and maybe even some of the continental basalt plateaus, are built,” said Jicha, who was not involved in the study.
Other oceanic plateaus, according to Sager, require more research. About the prospect of more massive shield volcanoes under the sea, he stated, “There may be approximately a dozen of these things down there.”
Although the Tamu Massif appears to be the world’s largest single volcano, Sager points out that there are other larger volcanic systems, such as the Siberian Traps, that may hold more secrets. Those features, unlike Tamu Massif’s creation, were most likely built out of molten rock from a variety of sources, he said.
What Caused The Volcano To Form?
Scientists are still attempting to figure out how Tamu Massif developed, according to Sager.
He believes the location on the seafloor had the proper combination of features, including a tectonic plate boundary, weak crust, and a source of hot magma below that may bubble up to the surface. As the molten rock cooled, it spilled out and built up a vast, steady elevation.
It’s unclear how the magma got to the surface in the first place. A glob of rock may have become superheated and then raised to the surface due to buoyancy. Alternatively, breaches in the crust above could have opened, enabling molten rock to escape.
According to Sager, the next stage will be to figure out where the magma came from. He wants to use a spacecraft equipped with GPS to return and measure the magnetic characteristics of the rock. According to him, the data will help him understand how the lava spread out.
“If it is genuinely one volcano, as the evidence suggests, the volume of magma that had to pass through the lithosphere [crust] is off the charts,” Jicha remarked.
