WASHINGTON — When you think of a gigantic volcano, you probably picture a mountainous structure reaching high into the sky and spewing lava. Researchers with the American Geophysical Union say that may not be the case in Alaska, where an undiscovered supervolcano may be lurking underwater. Their findings suggest that a chain of islands which are home to a group of smaller volcanoes are actually part of an enormous volcano structure that could have world-changing implications.

A team of researchers from several different institutions and disciplines say the Islands of the Four Mountains in the central Aleutians is home to six stratovolcanoes. These are what people generally think of when someone mentions a volcano. Stratovolcanoes can steep cone-shaped mountains which have a banner of ash and clouds at its summit. Like the famous Mount St. Helens in 1980, they can have powerful eruptions.

Although these are frightening events, researchers say a volcanic caldera falls into the same category of massive volcano that produce a super eruption which can cause severe global damage. The new AGU report theorizes that those six stratovolcanoes in Alaska (Carlisle, Cleveland, Herbert, Kagamil, Tana, and Uliaga) are all part of such a volcanic caldera, similar to the Yellowstone Caldera and other global supervolcanoes.

Supervolcano would be first discovered underwater

While stratovolcanoes tap into small or medium-sized supplies of magma, a caldera taps a huge reservoir of molten rock in the Earth’s crust. When the pressure on that magma supply exceeds the strength of the crust holding it in place, a giant explosion of lava and ash takes place.

Such an eruption doesn’t just blanket the area around the volcano but also disrupts the Earth’s atmosphere and can change the climate. Researchers believe such an eruption took place at the Okmok volcano in the year BCE 43. The destruction may have had long-lasting implications for the Roman Republic.

The study says if there is a caldera underneath the Islands of the Four Mountains, it’ll be even bigger than the one at Okmok. A supervolcano in the Aleutians would also be the first discovered underwater, according to Diana Roman of the Carnegie Institution for Science.

“We’ve been scraping under the couch cushions for data,” Roman says in a media release. “But everything we look at lines up with a caldera in this region.”

Still looking for proof

Despite all the signs pointing to something historic sitting under America’s largest state, the team says they still need more evidence to prove this theory is true.

“Our hope is to return to the Islands of Four Mountains and look more closely at the seafloor, study the volcanic rocks in greater detail, collect more seismic and gravity data, and sample many more of the geothermal areas,” says John Power, a researcher with the U.S. Geological Survey at the Alaska Volcano Observatory.

Study authors add that the Alaskan caldera theory would also explain why Mount Cleveland is so volcanically active. The stratovolcano is believed to be the most active volcano in all of North America over the last two decades.

“It does potentially help us understand what makes Cleveland so active,” Power adds. “It can also help us understand what type of eruptions to expect in the future and better prepare for their hazards.”

The findings were presented at the AGU’s Fall Meeting 2020.