POPOCATÉPETL VOLCANO, Mexico (AP) — In the predawn darkness, a team of scientists climbs the slope of Mexico’s Popocatépetl volcano, one of the most active in the world and whose eruption could affect millions. His mission: find out what’s going on under the crater.
For five years, the group from Mexico’s National Autonomous University scaled the volcano with pounds of equipment, risked data loss due to bad weather or a volcanic eruption, and used artificial intelligence to analyze seismic data. Now the team has created the first three-dimensional image of the interior of the 17,883-foot (5,452-meter) volcano, which tells them where the magma is accumulating and will help them better understand its activity and ultimately help authorities better respond to eruptions.
Marco Calò, professor in the volcanology department of the Geophysics Institute of UNAM and the leader of the project, invited The Associated Press to accompany the team on the latest expedition, the last before his research on the volcano is published.
Underground movement
Inside an active volcano, everything is moving: rocks, magma, gases and aquifers. Everything generates seismic signals.
Most of the world’s volcanoes that pose a risk to people already have detailed maps of their interiors, but not Popocatépetl, despite the fact that about 25 million people live within a 100-kilometer radius and homes, schools, hospitals and five airports could be affected by an eruption.
Other scientists took some early images 15 years ago, but they showed conflicting results and didn’t have enough resolution to see “how the volcanic edifice was built” and especially where the magma collected, Calò said.
His team increased the number of seismographs from 12 provided by Mexico’s National Disaster Prevention Center to 22 to cover the entire perimeter of the volcano. Even though only three can alert to an emergency, many more are needed to understand what is behind these emergencies.
The devices measure vibrations in the ground 100 times per second and generate data that Karina Bernal, 33, a PhD student and project researcher, processed using artificial intelligence to adapt algorithms developed for other volcanoes.
“We taught the machine about the different types of tremors that exist in El Popo,” and with that they were able to catalog the different types of seismic signals, she said.
Little by little, scientists began to deduce what kind of material was where, in what state, at what temperature, and at what depth. Later they were able to map it.
The result is far more complex than the drawings of volcanoes most have seen in school, with a main vent connecting a magma chamber to the surface.
This first three-dimensional cross-sectional image goes 11 miles (18 kilometers) below the crater and shows what appear to be different magma pools at different depths, with rock or other material between them and more numerous toward the southeast of the crater.
A “majestic” giant.
Popocatépetl emerged in the crater of other volcanoes in its current form more than 20,000 years ago and has been active since 1994, spewing plumes of smoke, gas and ash more or less daily. The activity periodically forms a dome over the main vent, which eventually collapses, causing an eruption. The last one was in 2023.
Calò, a 46-year-old Sicilian, speaks passionately about El Popo, as Mexicans call the volcano, peppered with trivia.
He explains that its height can change due to eruptions and tells how Popocatépetl in the first century had its own “little Pompeii” when a village on its flanks, Tetimpa, was buried in ash. In the early 20th century, human actions—using dynamite to extract sulfur from the crater—caused an eruption. And even though El Popo emits more greenhouse gases than almost any other volcano, its emissions are still a tiny fraction of what humans generate in nearby Mexico City.
For years, Calò studied volcanic activity from his computer, but trying to “understand how something works without touching it” caused a sense of disappointment, he said.
That changed with Popocatépetl, a volcano he describes as “majestic.”
To touch a volcano
After hours of walking up the flank of the volcano, Calò’s team sets up camp in a pine grove at about 12,500 feet elevation, a place apparently safe from pyroclastic explosions because the trees have managed to grow to significant heights.
A short distance up the mountain, the trees and bushes give way to ash and sediment.
They must cross a lahar, a mixture of rock and ash that during the rainy season becomes a dangerous mudslide, carrying away everything in its path. Now the dry clearing offers a spectacular view: to the east Pico de Orizaba—Mexico’s highest volcano and mountain—and the dormant volcano La Malinche; to the north, Iztaccíhuatl, a dormant volcanic peak known as the “sleeping woman”.
The sounds of Popocatépetl seem to multiply at night with the echoes. A rocket-like explosion might sound like it’s coming from one direction, but a puff of smoke from the crater belies the true source.
Karina Rodríguez, a 26-year-old master’s student on the team, said you can also hear small tremors in the ground or even ash falling like rain when the volcano is more active. On dark nights, the rim of the crater glows orange.
A natural laboratory
Direct knowledge of the volcano provides a much more objective understanding of the limits of their analysis, Calò said.
“We have a natural laboratory here,” he said. It is “very important to be able to understand and provide residents with detailed and reliable information about what is happening inside the volcano.”
At 13,780 feet (4,200 meters), backpacks full of computers, gas analysis equipment, batteries and water begin to weigh more and their pace slows.
Ash, dark and warm, dominates the landscape here.
At a seismographic station, the team pulls out the equipment and celebrates that it’s still working. They download his data and rebury it.
A “volcanic bomb”, a rock three and a half meters in diameter and weighing tons, marks the way and gives an idea of what the beginning of an eruption can mean. That’s why the upper area of the volcano is restricted, although not everyone pays attention. In 2022, a person died after being hit by a rock about 300 meters from the crater.
A bottle of tequila near a rocky outcropping known as El Popo’s navel hints at some of the traditions surrounding the volcano, including an annual pilgrimage to what some consider a nexus to the underworld.
The drive to continue climbing
Unearthing one of the last seismic stations, Calò’s face falls. The last recorded data is from the previous month. Battery died. Sometimes rats chew through machine wires or an explosion causes more serious damage.
The project has provided some certainty and, if repeated, will allow analysis of changes that will ultimately help authorities make better decisions when outbreaks occur.
But Calò says that, as always happens with science, it has also generated new questions that they will have to try to address, such as why the tremors are more frequent on the southeast side – where there is more accumulated magma – and what the implications might be.
This was the last expedition before their years of work to map the interior of the volcano were published. Watching the interior of the volcano move in 3D on a computer screen makes all the effort worthwhile.
“It’s what drives you to start another project and keep climbing,” said Rodríguez, the master’s student.