Toxic gases and ash from Mount Vesuvius took just minutes to asphyxiate an estimated 2,000 Pompeians in C.E. 79. A pyroclastic flow from Mount Pelée claimed the lives of nearly 30,000 on the Caribbean island of Martinique in 1902. If those catastrophic eruptions had occurred today, could scientists have forecast them in time to save lives?
Volcanologists have certainly made some progress on this front. Look no further than Popocatepetl, or El Popo. Lying on the outskirts of Mexico City, it is one of the largest active volcanoes in the world and one of the most heavily monitored volcanoes. Equipment used to keep tabs on El Popo, includes 10 seismic stations; five video cameras; two sonic sensors for evaluating the power of explosions; three hydrometeorological stations to measure rainfall and ash; five sensors to evaluate how the volcano physically deforms in the run-up to an eruption; and a thermal imaging camera.
Carlos Antonio Gutiérrez, research director of Mexico’s National Center for Prevention of Disasters, can monitor all the data collected by those devices from his phone. When Popocatepetl spewed smoke, ash and molten rock in May, Gutiérrez and his colleagues raised the threat level and fed local authorities real-time updates. Twenty-two million people live in the volcano’s shadow, and its ashfalls and eruptions are dangerous enough to cancel schools and shut down airports. Knowing that an ashfall or eruption will happen is vital, and Gutiérrez’s work helps people prepare for earthquakes or smothering ash clouds.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
In 1993 there was one sensor on El Popo. Forecasting was virtually nonexistent. When volcanic activity picked up ahead of the 1994 eruption that marked the start of Popocatepetl’s current behavioral pattern, nearby residents were convinced it would “be like Pompeii,” Gutiérrez says. He quickly placed more sensors on the volcano, which helped him and his team dispel misinformation and develop the warning system they use today.
In the past few decades, technological advances and an expansion of surveillance to more volcanoes have helped inform the more than 500 million people who live within the exposure range of one. Scientists are swimming in data; they just need to figure out what to do with this information in order to speed up their predictions. Today’s most accurate eruption forecasting systems dole out warnings in terms of hours rather than days or weeks. But many volcanoes display enough early behavioral clues that scientists often simply guess something is imminent ahead of the systems’ warnings—even if the precise moment of eruption is unclear. Researchers are optimistic that these warnings will eventually improve beyond mere hours’ notice.
These advances are vital. Volcanicactivity continues to threaten lives and communities across the globe.
“If you get it wrong, then the stakes are quite high,” says Tamsin Mather, a volcanologist and a professor at the University of Oxford. “If you tell them to evacuate, and then nothing happens, then the population will understandably not be as impressed next time when someone says, ‘You’ve really got to evacuate right now.’”
While current technology for detecting volcanic activity is “light-years” ahead of what was available in the 1990s, there are still a lot of unknowns, says U.S. Geological Survey seismologist Seth Moran. He compares the situation with a physician developing a diagnosis: Temperature, pulse and blood pressure are all symptoms of what’s happening inside a patient’s body, but sometimes doctors order a biopsy to look inside and find out what is really happening. “With volcanoes, we can’t do that,” Moran says. “You can’t go down and sample the magma that’s five miles below the surface.”
Until scientists develop a probe that can withstand magma sizzling at around 1,500 degrees Fahrenheit, more precise long-term eruption forecasts are unlikely to materialize. For now, volcanologists and seismologists need to stay vigilant, says Ken Hon, scientist-in-charge at the USGS’s Hawaiian Volcano Observatory.
“We have to really be on our game, even in the middle of the night,” Hon says. “This is not easy. There’s still a lot of human intuition involved in forecasting.”
A volcano erupts when gas or magma exits its main vent into the atmosphere or onto the surface. Magma drives these eruptions. Its movement can catalyze gas emissions, spur earthquakes and deform the volcano’s exterior. These signs, in addition to low-frequency sounds below human hearing thresholds, are the main indicators that scientists use to forecast volcanic activity and eruptions.
Several instruments deployed around volcanoes measure these telltale signs. The devices include seismometers that look a little like coffee cans and monitor for any ground shaking that would signal ascending lava. Others resemble Home Depot plastic bins containing computers and car batteries;these record the seismometer readings and keep scientists apprised from a distance. Newer technologies capture seismic energy—how the earth moves—in three dimensions rather than just one.
Above all else, these instruments must be sturdy. “It's challenging because you’re putting all these very sensitive electronics in an environment that’s very harsh. It’s windy; it’s rainy; often there’s sort of acid gas in the air,” says Diana Roman, a volcanologist at the Carnegie Institution for Science in Washington, D.C. “We’ve learned over the years how to build these in the way that they last.”
With such a profusion of instruments, a volcano rarely erupts without scientists having some sort of heads-up. Whether it’s seismic activity or a spurt of carbon dioxide, most volcanoes emit warning signs that scientists use to make pretty accurate forecasts in the hours prior to an eruption. Experts say it is tempting to speculate these advances could have saved the ancient Pompeians from disaster, but not all volcanoes offer clues. Some just erupt without any warning.
Scientists don’t fully understand what initially triggers an eruption or what causes a volcano to go from restlessness to “actually throwing stuff out of the ground,” says Erik Klemetti, an associate professor of earth sciences at Denison University. Knowing what kick-starts the magma to pool and then rise in the chamber would help scientists create better, timelier forecasts.
Part of the unknowns revolves around the many kinds of volcanoes that exist. If a volcano does not have an open vent, scientists can’t assess volcanic activity via gas emissions. Some volcanoes swell up like an inflated balloon right before they erupt, a ground shift that is easily captured with satellites. Others, such as Kilauea on the Big Island in Hawaii, bulge by only millimeters (one twenty-fifths of an inch).
“We've made massive progress, and satellites are really helping us. But we’re still, like, interpreting the messages from the deep,” Mather says. “We can't see the full picture.”
Furthermore, volcanoes are finicky. They don’t just change behavior; they also change their patterns of behavior. Days of earthquakes preceded Kilauea’s 2018 eruption, which gave the USGS Hawaiian Volcano Observatory staff ample time to inform Big Island officials. But when Kilauea erupted in early June, Hon’s team only had an hour’s notice.*
“We’re not going to change the fact that our volcanoes don’t send us a signal until right before the eruption,” Hon says. “That’s the nature of the beast, right? It’s just sitting there, and then it strikes. So we just have to be ready on that sort of timescale to take that on and identify it accurately.”
There are some signs of progress. Italian scientists created an automatic warning system that successfully predicted 57 out of 59 eruptions of Mount Etna (though just around an hour ahead of time) over a period of nearly a decade starting in 2008. And in 2021 researchers at NASA’s Jet Propulsion Laboratory and the University of Alaska Fairbanks claimed they found warning signs on five volcanoes years in advance by analyzing heat signatures beneath the behemoths.
The next obstacle for volcano eruption forecasts is determining an eruption’s strength. Moran says he thinks the increase in available data will help solve this mystery, leading to more helpful forecasts for local communities.
“It’s not sufficient for us to write papers and call it good,” Moran says. “We have to be out in the communities, spreading the word and making sure that the information we have is understandable—and is understood by those who need to know it.”
*Editor’s Note (7/12/23): This paragraph was edited after posting to correct the description of the Kilauea eruption that was preceded by days of earthquakes.