According to evidence presented at the fall meeting of the American Geophysical Union next week, the trail of volcanic islands off the coast of southern Alaska may indeed be part of a single vast caldera. If so, it is possible that the catastrophic dwarf eruption of Mount St. Helens in 1980 erupted in a large enough volume to erupt a huge amount of newly declared volcano.
The behemoths in question are marked by a semicircular cluster of peaks in the Aleutian Islands, called the Islands of the Four Mountains (IFM). Long thought to be an independent volcano, with six peaks – including Herbert, Carlisle, Cleveland, Tana, Uliaga and Kagamil – it could actually be a range of prey attached to the edges of many large volcanoes.
If this idea is confirmed, however, the results do not necessarily predict future destruction.
U.S. “This new research result will not change the crisis,” said Alaska Volcano Observatory, which will present the work Monday at a meeting of geological survey geologist John Power and the AGU. “We’re not predicting anything dangerous here.” (Learn more about supervicular oes and why this term can be misleading.)
Looking for Behemoth
When scientists first visited IFM in 2014, they were not prepared to find evidence for a massive eruption, but instead focused on archeology in the area. During the next few years another group stepped forward to investigate the volcanic tectonic underpinnings.
The researchers examined local geology and used several groups of techniques to study the field, including seismometers to select small irrigation and chemical analysis to understand the composition of gases affecting the soil. While they were working through the data, however, the surprising features they only recently realized were associated with a tremendous and ancient explosion.
The first puzzle piece was a strange half-ring shape of a closely clustered IFM volcano. One explanation could be cal ladra.
When a huge reservoir of magma suddenly empties and the soil breaks down, Cal Laderas is formed, creating huge tensions anywhere from one to miles0 miles above the Earth’s surface. The formation of caldera forms many fractures through which magma can then come to the surface, so volcanic clusters are common around their edges or centers.
In this case, the researchers suspected that the IFM volcano could potentially represent a series of connected geological formations around a 12-mile-wide cal ladera, which they thought was hundreds of feet below the surface of the frigid Pacific waters.
“This would be an easy problem if it were on the ground,” says Diana Roman, a volcano and director investigator at the Carnegie Institution for Science. “But it’s underwater, so it makes it more difficult to order its intensity.”
The second part of the puzzle was the discovery of rocks called welded ignibrits. This material forms when a large eruption, the volcanic ash, sings so much. Laying grain is welded into a fairly solid rock, explains Pete Stalling, who participated in the 2015 research season, but is not part of the new analysis.
Encouraged by this puzzling data, the team began “cutting the cushion” to find any other information to help explain the incident. They collected an array of evidence, including gravitational anomalies, from satellite data and bathimetric surveys conducted in the area immediately after World War II. Although not high resolution, seafloor mapping indicated many curved ridge structures and deeper depths over 400 degrees that could be part of the caldera.
If their suspicions are confirmed, the team believes a potential underwater basin could result from a volcanic eruption that was shy of revenue from a label called “Super Eruption.”
“Any one of these pieces of evidence is questionable,” Power says. “But as we line up more and more, it becomes a stronger argument.”
Bigger, but not the biggest
The team warns that many unknowns remain about the composition. For one, they are still unsure about the size of the caldera, and they don’t know if it was a big explosion or some small outbreak.
If it were a single event, it would be a medium-sized explosion by geological history, Roman notes, compared to the rest of the world. For example, in a very rough calculation, an IFM would explode at one-tenth the size of the person who struck Yellowstone F40,000 years ago, says Adam Kent, a volcanologist at Reg Reagan State University who is not part of the study team. “It will potentially be world-changing,” he says. “But the world is not the end.”
Nevertheless, early research provides some tentative links to help scientists better understand current and potential future threats in the field.
“This sets a really good story for future investigation,” says Jackie Kaplan-erb Rabach, a volcanologist and seismologist at Washington University in the West, who was not part of the research team.
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