Tamu Massif, a well-known undersea mountain off Japan, turns out to be one continuous shield volcano, about the size of New Mexico or the British Isles, said geophysicist William W. Sager, lead author of a study published online this week in the journal Nature Geoscience.
Sager and team members had long ago given names to the formations jutting up from the Shatsky Rise, a California-size oceanic plateau southeast of Japan. Tamu, the largest of three major features, stands for Texas A&M University, where Sager conducted his research for two decades before moving recently to the University of Houston.
Tens of thousands of seamounts pock the ocean floors around the world, and others may be larger, such as the Ontong Java Plateau near the Solomon Islands and the Kerguelen Plateau in the southern Indian Ocean.
But thus far, none appears to be a single basalt shield volcano, but rather a composite of many such volcanoes, Sager said.
“One of the real things you have as a marine geologist or marine geophysicist is that these things have found a good place to hide,” Sager said. “It’s easier to study something on the surface of Mars in many ways than it is to study something that’s right out there in the ocean. It’s not like we didn’t know that there was something out there.
“It’s just taken generations to get the time and money and to focus on it and get out there and study it.”
Sager’s team drilled core samples from the volcano, jutting from the ocean floor about 4 miles deep.
Tamu rises about as high as many peaks of the Sierra Nevada — more than 13,000 feet. But much of its mass has sunk into the ocean crust, making it far shorter than Olympus Mons, which towers about 13 miles from the more rigid Martian surface.
But Tamu appears to have a larger base.
Olympus Mons is about 374 miles in diameter, according to NASA; Tamu spans about 403 miles at its widest point and covers about 8,000 more square miles, according to the study.