The world's largest volcano has been found at the depths of the Pacific Ocean, says a new study.
Researchers are calling the giant underwater mound, Tamu Massif, and it is 400 miles wide and 2.5 miles high.
That makes it as large as the British Isles.
The volcano is off the coast of Japan in the northwest Pacific, 6,500 feet below the sea.
Tamu Massif is far larger than even the next largest volcano discovered, Mauna Loa near Hawaii and is only 25 percent smaller than Olympus Mons on Mars - the biggest volcano in the Earth's solar system.
More from GlobalPost: Japan's Sakurajima volcano erupts, coating town in ash (VIDEO)
“Olympus Mons is the 800-pound gorilla of the solar system,” said study author William W. Sager, of the University of Houston.
“We didn’t know these massive volcanoes were here on Earth.”
The volcano erupted 144 million years ago and was subsequently extinct, according to lava samples taken over the years.
For years scientists believed that Tamu Massif was simply an oceanic plateau known as the Shatsky Rise.
Though oceanic plateaus were formed by lava, they are not considered single volcanos.
The study was published in the journal Nature Geoscience.