Scientists obtain first 3D images inside Mexico’s Popocatépetl volcano

POPOCATEPETL VOLCANO, Mexico. In the predawn darkness, a group of scientists climbs the mountainside. Mexico Popocatepetl volcano, one of the most active in the world, whose eruption could affect millions of people. His mission: to find out what is happening under the crater.

For five years, a group from the National Autonomous University of Mexico climbed to the top. volcano with kilograms of equipment, risked losing data due to bad weather or a volcanic eruption and used artificial intelligence for seismic data analysis. Now the team has created the first 3D image of the interior of the 17,883-foot (5,452-meter) volcano, which tells them where magma accumulates and will help them better understand its activity and ultimately help authorities better respond to eruptions.

Marco Calo, a professor at the Department of Volcanology at the UNAM Institute of Geophysics and the project leader, invited The Associated Press to accompany the team on its latest expedition, the last before the results of the volcano's research are published.

Inside an active volcano, everything moves: rocks, magma, gas and aquifers. All this generates seismic signals.

Most of the world's volcanoes that pose a danger to humans already have detailed maps of their interiors, but not yet Popocatepetl, despite the fact that about 25 million people live within a 62-mile (100-kilometer) radius and the eruption could damage homes, schools, hospitals and five airports.

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 where the magma collected in the first place, Calo said.

His team increased the number of seismographs from 12 provided by Mexico's National Center for Disaster Prevention to 22 to cover the entire perimeter of the volcano. Even though only three people can warn of 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 doctoral student and researcher on the project, processes using artificial intelligence to adapt algorithms developed for other volcanoes.

“I told the machine about the different types of tremors at El Popo,” and from that they were able to catalog the different types of seismic signals, she said.

Little by little, scientists began to draw conclusions about what materials were located where, in what state, at what temperature and at what depth. Later they managed to put it on a map.

The result is much more complex than the drawings of volcanoes most people saw in school, with the main vent connecting the magma chamber to the surface.

This first 3D cross-sectional image extends 11 miles (18 kilometers) below the crater and shows various pools of magma at varying depths, with rocks or other material between them and more numerous ones southeast of the crater.

Popocatépetl, in its current form, emerged from the craters of other volcanoes 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..

Calo, a 46-year-old Sicilian, speaks passionately about El Popo, as the Mexicans call the volcano, rattling off trivia.

He explains that its height can change due to eruptions, and tells how Popocatepetla had its own “little Pompeii” in the first century when a village on its slopes, Tetimpa, was buried in ash. In the early 20th century, it was human action—using dynamite to extract sulfur from the crater—that triggered the eruption. And while El Popo emits more greenhouse gases than any other volcano, its emissions are still only a fraction of what people in neighboring Mexico City produce.

For years, Calo studied volcanic activity from his computer, but trying to “understand how something works without touching it” led to frustration, he said.

That changed with the appearance of the Popocatépetl volcano, which he calls “majestic.”

After several hours of walking along the side of the volcano, Kahlo's team sets up camp in a pine grove about 12,500 feet above sea level, apparently safe from pyroclastic explosions since the trees have managed to grow to considerable heights.

A little higher up on the mountain, trees and bushes give way to ash and sediment.

They have to cross a lahar – a mixture of stones and ash, which during the rainy season turns into a dangerous mudflow, destroying everything in its path. Now the dry clearing offers a breathtaking view: to the east, Pico de Orizaba – the highest volcano and mountain in Mexico – and the extinct volcano La Malinche; to the north is Iztaccihuatl, a dormant volcanic peak known as the “sleeping woman.”

The sounds of Popocatepetl seem to multiply at night along with the echoes. The rocket-like explosion may sound like it's coming from one direction, but the plume of smoke from the crater obscures the real source.

Karina Rodriguez, a 26-year-old master's student on the team, said you can also hear small tremors of the ground or even falling ash, similar to rain, when the volcano is more active. On dark nights, the edges of the crater glow orange.

According to Calo, direct knowledge of the volcano gives a much more objective view of the limits of their analysis.

“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), their backpacks full of computers, gas analysis equipment, batteries and water begin to weigh more and their pace slows.

Here the landscape is dominated by ash, dark and warm.

At the seismographic station, the team digs up the equipment and notes that it is still working. They download his data and rebury him.

A “volcanic bomb” – a stone one and a half yards in diameter and weighing tons – marks the path and gives a clue to what the start of an eruption might mean. This is why the upper part of the volcano is limited, although not everyone pays attention to this. In 2022, a person died after being hit by a rock about 300 yards (meters) from the crater.

A bottle of tequila near the rocky depression known as El Popo's navel hints at some of the traditions surrounding the volcano, including an annual pilgrimage to what some consider a point of communication with the underworld.

When Kahlo digs up one of the last seismic stations, Kahlo's face falls. The latest data recorded is from months ago. The battery is dead. Sometimes rats chew through car wires, and the explosion causes more serious damage.

The project provided some reassurance and, if replicated, would allow changes to be analyzed that would ultimately help authorities make better decisions in the event of eruptions.

But Calo says that, as always happens with science, it has also raised new questions that they will have to try to answer, such as why tremors occur more often on the southeast side – where there is more accumulated magma – and what consequences that might have.

This was the last expedition before the publication of their many years of work mapping the interior of the volcano. Watching the inside of a volcano move in 3D on a computer screen makes all the effort worthwhile.

“It’s what drives you to start a new project and keep climbing,” says Rodriguez, a master’s student.