Sometimes, volcanoes' summits collapse, forming miles-wide depressions called calderas, which are peppered by eruptive vents. When rivulets of magma force their way out of these vents, those small eruptions can spew dangerous amounts of lava and gas.
But the locations and threat levels of these vents are difficult to predict – eruptions can sometimes occur miles from the caldera's center. That leaves cities located on or near volcanic fields, like Naples, Italy, facing a constant risk of poisonous volcanic gas, ash, and explosive bursts of lava.
Now, however, a group of scientists have figured out how to accurately pinpoint where on a volcano's surface or in a caldera's volcanic fields these damaging vent eruptions are likely to occur.
"Calderas have fed some of the most catastrophic eruptions on Earth and are extremely hazardous," the scientists wrote in a new study published Wednesday in the journal Science Advances. That hazard is often underestimated by local populations, they added.
Mount Kilauea in Hawaii, which erupted last year, is speckled with such vents. The eruptions forced nearly 1,500 people to flee their homes, CBS News reported.
"These vents have lava coming out of them like fountains, which then leaks across the landscape like a slug," Eleonora Rivalta, the lead author of the study, told Business Insider.
The scientists hope that insights from their new model could help communities like Hawaii's better prepare for and anticipate future eruptions.
Magma's fickle pathways
Magma, the liquid or semi-liquid rock under the Earth's crust, makes up most of our planet's mantle (its intermediary layer). When magma pushes its way to the surface, that causes a volcanic eruption.
Magma likes to take the path of least resistance as it surges upward. So figuring out what that path is can enable scientists to predict where it will next breach our planet's surface. That's what Rivalta's team set out to do.
The easiest path, the researchers found, is for magma to move through rocks that are more "stretched out" than their nearby counterparts – less compressed, in other words.
Although many geologists thought the path of least resistance would be through an existing pathway or fault, Rivalta's team found that vents are often "single-use only", meaning magma erupts through them once and never again.
Rivalta and her colleagues used these discoveries to make computer models of future magma paths to the surface. They compared the predictions of their model to the known eruptive behaviour of vents across Italy's Campi Fleigrei, outside of Naples.
This 8-mile-wide active volcanic field – known as the "burning fields" – first erupted almost 50,000 years ago, though the most recent major eruption was in 1538.
Rivalta's model accurately mapped Campi Flegrei's 70 eruptions over the past 15,000 years, including the highly damaging Monte Nuovo eruption in 1538.
Predicting the next Yellowstone eruption
Between 1600 and 2017, 278,880 people around the world were killed by volcanic activity and the consequences of those eruptions, like starvation or tsunamis.
Since the 1980s, deaths related to volcanic eruptions have been rather limited, as geographer Matthew Blackett reported in The Conversation. This isn't because scientists have gotten better at predicting eruptions – it's a matter of chance, since recent eruptions have been far from heavily populated areas.
So Rivalta hopes to leverage her group's new research to give cities like Naples more information about impending eruptions. She also wants to apply this new model to Mount Etna in Sicily, and use it to examine the supervolcano under Yellowstone National Park.
That enormous volcano last erupted more than 640,000 years ago. If it were to erupt again, the supervolcano would spew ash across thousands of miles of the US.
Following the Yellowstone volcano's last eruption, it collapsed on itself, creating a 1,500-square-mile caldera that's ripe for new appearances of magma.
"Yellowstone is a caldera with tons and tons of vents," Rivalta said. "The question of where the next one might appear is very relevant to this caldera."
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