Cluster of Aleutian peaks could be single supervolcano, scientists say

Aerial photograph of volcanoes of the Islands of Four Mountains: Mount Tana is in the foreground and Mount Herbert, Mount Cleveland, and Mount Carlisle are shown left to right in the background. (John Lyons/USGS)

In a new study, scientists said a string of volcanic Aleutian islands could be part of a single, massive undiscovered volcano.

While scientists have been compiling their research for six years, there’s still a lot to piece together, said Diana Roman, a volcanologist with the Carnegie Institution for Science in Washington, DC.

“This is a little bit like trying to put together a 2,000-piece jigsaw puzzle, where half of the pieces are missing, and you don’t have the box, so you don’t know what it’s going to look like.”

Roman is one of a number of scientists from across the country studying whether a giant volcano is hiding beneath the Islands of Four Mountains — a string of eight volcanic islands in the central Aleutians, about 170 miles west of Unalaska

The scientists presented their research at the American Geophysical Union’s Fall Meeting on Monday.

A map of Alaska with a series of black triangles along the aleutians
Map of the Aleutian Volcanic arc shows the positions of volcanoes (black triangles) and the location of the Island of Four Mountains. (Alaska Volcano Observatory)

John Power is a geophysicist with the U.S. Geological Survey at the Alaska Volcano Observatory, who co-led the presentation at the virtual conference this week. He said research on the Islands of Four Mountains started in 2014 because of frequent eruptions at Mount Cleveland, which occupies the entire western half of Chuginadak Island.

“Mount Cleveland, over the last 20 years — and perhaps much longer — has been the most persistently-active volcano in North America,” Power said.

AVO scientists have struggled with improving warnings about potential eruptions at Mount Cleveland because it is so active, according to Power. But after studying the large stratovolcano and five others nearby, multiple pieces of evidence led them to conclude there might be a 12-mile-wide caldera — a large volcanic crater — or a number of calderas, hidden underwater beneath the group of islands. That could help explain the frequent explosive activity seen at Cleveland, Power said.

The scientists found evidence including ignimbrites, a special type of rock formed from large, catastrophic caldera-forming events; a slight change in gravity where the caldera might be; extensive geothermal and hot springs throughout the islands; frequent earthquake activity; and most notably, Power said, the semi-circular arrangement of the islands which might form the caldera’s rim.

“There are multiple pieces of evidence that have come together, that make us think this is also a very large, caldera-type volcano, which was previously unrecognized for two reasons. One is that we all know the Islands of Four Mountains are very remote, and the volcanoes there have not received a lot of prior study,” Power said. “And, in this case, much of the caldera structure is likely under the Bering Sea, so it’s been hard for people to identify.”

But Power and Roman said the caldera’s existence is not yet proven. To find out if the islands form one big crater, or whether there are multiple calderas side by side, or even if there’s a caldera there at all, they’ll have to return to the Islands of Four Mountains to gather more evidence to fully test their hypothesis.

A woman standing on a barren tundra field leans over some scientific equipment. The ocean is visible in the background
Carnegie postdoc Amanda Lough (now at Drexel University) inspects a seismic station on Cleveland Volcano. (Diana Roman/Carnegie Institution for Science)

If the researchers’ suspicions are correct, the newfound volcanic caldera would become the first discovered in the Aleutians that’s hidden underwater. It would belong to the same category of volcanoes as the Yellowstone Caldera, and others who’s super-eruptions have triggered profound global consequences.

One of those, Power said, was the eruption of the Aleutian volcano Okmok, in the year 43 B.C., recently implicated in the fall of the Roman Republic.

“If you look at some of the other large caldera-forming eruptions — such as Okmok  — you do see these have resulted in cooling of the climate,” Power said. “In 1815, there was a very famous eruption at [Mount] Tambora in Indonesia, about this size, that resulted in what’s called the ‘year without a summer’ — there were crop failures, pandemics.”

According to Power, understanding where and when large volcanic eruptions occur is important in understanding the global impact they have, but there’s no immediate concern there will be a super-eruption under the Islands of Four Mountains.

Rather, he said, knowing a potential caldera system is there will help agencies such as the AVO anticipate future eruptive activity, and identify hazards it may pose to aircraft, fishermen, and nearby communities such as Nikolski and Unalaska. 

“It does not mean that there will be a huge eruption coming from this caldera anytime soon,” Power said. “It may be thousands of years or potentially never.”

Scientists are currently planning their next expedition to the Islands of Four Mountains, which could be several years out, Roman said. The last major expeditions to the islands were in 2014, 2015, and 2016.