A mysterious supervolcano that has not been discovered before may be lurking beneath the Aleutian Islands of Alaska.
A new study suggests that a large crater, created when the supervolcano erupted, connects at least four existing volcanoes. It is so large that if the supervolcano erupted over the past thousands of years, it could disrupt civilizations around the world, says John Power, a geophysicist at the Alaska Volcano Observatory's Geological Survey. Power presents the findings at the annual meeting of the American Geophysical Union on December 7th.
The discovery, not yet confirmed, came from several tests that at first glance seem unrelated, says Diana Roman, a volcanologist at the Carnegie Institution for Science in Washington, D.C. “There’s no one who smokes a gun,” she says. And, in fact, the islands of the Four Mountains with mythical sound, actually six volcanoes located near the center of the island chain, look like a common volcanic cluster.
But on the whole, the data convincingly point to the existence of a boiler about 20 kilometers wide. The peaks of the volcanoes are arranged in a ring and the bathymetric mapping of the seabed, mostly from the 1950s, shows arched mountain ranges and a depression 130 meters deep in the center of the ring. Both are indications that volcanoes are connected by a large caldera, a huge crater that forms when a very large magma chamber in a volcano explodes and empties.
The gravity data from the satellites echoes the appearance of other boilers. And the analysis of such volcanic gases as sulfur dioxide, as well as patterns of micro-earthquakes also suggest the presence of a boiler.
“We weren’t surprised that there were micro-earthquakes,” Roman says, considering that one of the volcanoes, Mount Cleveland, is one of the most active volcanoes in the Aleutians. But, she says, those micro-earthquakes have spread further east and north than they would expect based on the volcanoes seen on the surface. "That makes more sense in the context of the boiler."
One of the hallmarks of many boilers is the volcanoes still active at their edges that access the same magma chamber, even long after the boiler itself has formed. Mount Cleveland fits into that scenario. “It’s exploded 60 or 70 times since 2001,” Power says. In addition to popping ash feathers high in the sky that disrupt air travel (SN: 11/27/18), this constant level of activity is typical of volcanoes bordering other known boilers. One of these volcanoes is the Indonesian Rinjani, whose eruption around 1257 released enough sulfur particles to cool the entire planet (SN: 14/06/12).
Gathering the evidence was a challenge, thanks to the extremely remote location, a largely underwater environment, and younger volcanic deposits that darken the older ones. In addition, separate studies provided different lines of evidence for a supervolcano boiler, but none connected the points. Roman compares the team's approach to "looking under the sofa cushions."
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“It’s a good example of how many threads come together to make a bigger story,” says Michael Poland, a volcanologist at the USGS Yellowstone Volcano Observatory who did not participate in the study. "We're starting to get the data sets we need to make these kinds of discoveries."
The Aleutian site is accessible for a short time each year, says Poland, so "it's crazy to pick up data." But that is exactly what the team hopes to do to confirm the existence of the boiler. He also plans to look for matching ashes in ice cores collected in other parts of the world to determine when the supervolcano would have erupted. “These very large boilers have very large impacts globally,” Power says. "This potential identification helps us understand what to expect, why Cleveland is so active, and to understand the dangers."