For the first time, The interior of Popocatépetl has been mapped in three dimensions With an unprecedented level of detail, a team from the National Autonomous University of Mexico (UNAM) has managed to construct a 3D image of the volcano's subsurface, showing how magma is distributed beneath one of the most active and closely monitored volcanoes on the planet.
This advance comes after five years of high-altitude expeditions, continuous seismic measurements and data processing supported by techniques of Artificial IntelligenceThe result is not only a spectacular image, but a key tool for improving risk management in a region where people live close to 25 million people within a 100-kilometer radius, with strategic infrastructure such as airports, hospitals, and educational centers.
How the interior of Popocatépetl has been seen in 3D
The project, led by Marco Calò, volcanologist at the UNAM Institute of GeophysicsIt stems from a simple but difficult-to-implement idea: harnessing ground vibrations to "take an X-ray" of the volcano. Every small tremor, every quake, and every explosion generates seismic signals that spread through the interior and change according to the type of material they encounter.
Until now, Popocatépetl was an exception among the world's large active volcanoes: It did not have a high-resolution internal mapDespite its intense activity since 1994 and its proximity to densely populated areas, the first attempts, about 15 years ago, yielded only partial images and, occasionally, contradictory results regarding the internal structure and the location of magma reserves.
To overcome these limitations, the team decided to reformulate the surveillance strategy. The instrumentation network was expanded, and modern data analysis techniques were adopted, with a focus on obtain a robust three-dimensional model of the subsoil capable of answering key questions: where magma is concentrated, how it connects to the crater, and which areas are most likely to generate seismicity.
The challenge wasn't just scientific. Every measurement involved climbing the slopes of Popocatépetl with backpacks loaded with equipment In a changing environment, with ash, gases, and the constant risk of minor explosions, this combination of fieldwork and advanced data analysis has been key to arriving at the final picture.
A network of seismographs and artificial intelligence at the service of the volcano
One of the pillars of the project was the expansion of the seismic network surrounding the volcanoPopocatépetl had a dozen monitoring stations operated by the National Center for Disaster Prevention (CENAPRED). For this research, the UNAM group increased the number of stations to 22 seismographs distributed around the crater, covering the perimeter with much greater density.
These devices record ground vibrations up to one hundred times per secondThat level of detail generates an enormous volume of data, impossible to analyze manually in a reasonable timeframe. That's where artificial intelligence comes in: the PhD student. Karina Bernal adapted algorithms designed for other volcanoes and taught the machine to recognize the different types of tremors characteristic of Popocatépetl.
Through this training, the following were built seismic signal catalogs These signals range from small microseisms to events associated with fluid movement, explosions, or rock fracturing. Each type of signal provides different clues about what is happening deep underground, allowing us to go beyond simply recording "whether or not there is an earthquake."
By combining information from the 22 stations and the patterns identified by the algorithms, the researchers were able to to infer what materials are present in each zone inside the volcano...in what state they are (solid, partially molten, or molten), at what approximate temperature, and at what depth. With all this information, the following was generated: three-dimensional seismic tomography of Popocatépetl.
This type of modeling is similar to a medical CT scan, except that here, instead of X-rays, seismic waves traveling through the volcano are used. Where the waves slow down, there is a higher probability of activity. hot material or magma; where they accelerate, the coldest and most compact rocks dominate.
What the 3D seismic tomography of Popocatépetl reveals
Far from the simplified scheme that appears in school books—a volcano with a single vertical vent and a well-defined magma chamber—the model obtained shows a much more complex internal systemThe three-dimensional image extends to 18 kilometers below the crater and draws a network of zones with different physical properties.
According to the UNAM team, the tomography indicates what appear to be several "pockets" or reservoirs of magma at different depths, separated by more solid material which acts as a partial barrier between them. It is not, therefore, a single uniform chamber, but a segmented system with different magmatic bodies connected more or less efficiently.
One of the most striking findings is the higher concentration of magma towards the southeast sector of the volcanoThis area coincides with more abundant seismicity, suggesting that particularly active internal processes are taking place there: fluid movement, pressure changes, and possible preferred routes of magma ascent.
This internal distribution helps to reinterpret some patterns of activity observed on the surface, such as the frequency of gas and ash emissions, subtle deformations of the volcanic edifice, or certain seismic swarms. Although it still does not allow us to predict exactly when an eruption will occur, it does offer a much more robust physical context in which to assess the evolution of the system.
Furthermore, the tomography reinforces the idea that Popocatépetl is a dynamic volcano in continuous internal reorganizationwhere magma can redistribute among reservoirs and modify activity patterns over time. Repeating the same type of studies in the future will allow for image comparisons and the detection of relevant changes before major eruptive episodes.
A powerful, active giant with a history and a risk to millions of people
Popocatépetl, colloquially known as "The Popo", it rises up to the 5.452 meters and dominates the landscape of central Mexico. Its current form was consolidated more than 20.000 years, when it emerged in the crater of ancient volcanoes, and from 1994 remains in a state of almost continuous activity, with columns of gas, ash and small explosions frequently recorded.
This activity is not just a scientific matter: the volcano has a radius of influence of around 100 kilometers where millions of people live and operate five airportsas well as schools, hospitals, and other critical infrastructure. Changes in the alert level can directly affect flights, preventative evacuations, or access restrictions to certain rural and tourist areas.
The history of Popocatépetl is punctuated by episodes that illustrate its destructive power. In the 1st century, the town of Tetimpa was buried under volcanic ash...in what researchers have described as a kind of Mesoamerican "mini Pompeii." Already in the 20th century, human intervention, with the use of dynamite to extract sulfur from the craterIt even triggered an eruption, reminding us that industrial activity in volcanic areas is not without consequences.
Despite being one of the volcanoes that The region emits more polluting gases.Its emissions represent only a fraction of what neighboring Mexico City generates. This contrast puts into perspective the relative weight of volcanoes compared to human activities in the global greenhouse gas balance, a topic of growing interest in Europe as well.
The last significant eruption was recorded in 2023Within this pattern of intermittent activity that necessitates constant monitoring, the new 3D model is now integrated into this daily tracking effort, contributing Additional information for interpreting the signals coming from the monitoring network and complement the activity report and alert.
Living and working in a "natural laboratory" at 4.000 meters
Beyond the data, the project has been an intense experience for the scientific team. Calò himself, who for years studied volcanoes solely from a computer, acknowledges that working directly on the slopes of Popocatépetl It has changed his perception of the investigation. Going from on-screen graphics to the actual sound of explosions and the smell of sulfur opens up another way of understanding the system being analyzed.
The expeditions begin at dawn, with several hours of ascent to find a suitable place to set up camp, usually in a pine forest area around 3.800 metersThe presence of tall vegetation is a sign that explosions rarely reach that far and that the area is reasonably safe for overnight stays and acclimatization.
From that point on, the landscape changes. The trees gradually give way to scattered scrubland among volcanic ash and, further up, to terrain almost entirely covered by loose sediment. Along the way, you have to cross a lavaa tongue of stones and ash that, during the rainy season, transforms into a river of mud capable of sweeping away everything in its path. Outside of those times, the dry riverbed offers a privileged viewpoint of other emblematic volcanoes, such as the Pico de Orizaba, La Malinche or Iztaccíhuatl.
For those who participate in the campaigns, such as the master's student Karina RodriguezThe work combines the analysis of seismic waves with the physical experience of "feeling" the volcano: to hear the ash falling like rain, notice the vibration of the ground during a small earthquake or see how an orange glow illuminates the crater on the darkest nights.
The altitude adds an additional difficulty. From the 4.200 metersThe backpacks loaded with laptops, gas analysis equipment, batteries, and water containers seem to weigh much more, and the team's pace slows down. Even so, on many occasions it is necessary to carry up to 50 kilos of material When a new seismographic station is installed, it turns each campaign into an exercise in physical as well as intellectual endurance.
Buried stations, volcanic bombs and hillside traditions
An important part of the fieldwork consists of periodically check the seismic stationsEach time the team arrives at one, they must locate and unearth it—they are hidden underground precisely to avoid theft or direct damage—, check that the electronics are still operational, verify the status of the solar panel, download the data, and cover it again.
There isn't always good news. On more than one occasion, researchers have discovered that The battery at one of the stations had failed months ago. or that small animals had gnawed through the cables. In more extreme situations, some installations have been hit by fragments ejected during explosions, resulting in serious damage or destruction.
The landscape is notable for its distinctive features. "volcanic bombs"Large boulders, up to a meter and a half in diameter and weighing several tons, have been ejected by the volcano in previous eruptions. One of these boulders even marks the path to the summit and serves as a reminder of what the start of a more powerful eruption could entail.
For safety reasons, the area near the crater is officially restricted, although this is not always fully respected. In 2022, a person died after being hit by a rock about 300 meters from the edge, an incident that underlines the need to respect access restrictions around an active volcano.
Alongside this context of risk, Popocatépetl also keeps alive local traditions and cultural elementsNear a hollow known as the "Popo's Navel" It's common to find remnants of offerings, such as a bottle of tequila, linked to annual pilgrimages to a spot many consider a symbolic connection to the underworld. This intersection of science, myth, and everyday life is part of the typical landscape on the volcano's slopes.
What changes for volcanic risk management
Obtaining the First detailed 3D image of the interior of Popocatépetl It is not merely an academic achievement. It has practical implications for risk management and emergency preparedness, both in Mexico and in other countries with active volcanoes, including several in Europe.
Have a well-defined internal model It allows for a more precise correlation of signals observed on the surface—such as changes in seismicity, ground deformation, or variations in the type of eruptions—with specific processes occurring at depth. For example, if an increase in tremors is detected in the southeastern area of the craterwhere tomography reveals a greater accumulation of magma, authorities can assess that change with more physical context.
The project also demonstrates the potential of combining dense networks of seismographs with artificial intelligenceThis approach is already on the radar of volcanic monitoring centers worldwide. For Europe, where volcanoes like the Etna, Vesuvius, the Phlegraean Fields or the volcanic systems of Iceland They are the subject of constant attention; this type of methodology offers a concrete reference for how to improve the resolution of internal models.
Furthermore, repeating the same type of tomography in the future, with the seismographs already installed and the algorithms refined, will open the door to compare the internal structure of the volcano at different timesAny significant change in the distribution of partially melted zones or in the connectivity between reservoirs may be an early sign that the system is reorganizing itself before a new eruptive cycle.
The researchers insist, however, that No model allows for predicting eruptions with complete accuracy.What these tools do provide is a much more solid basis for interpreting daily data and making informed decisions about changes in alert levels, air restrictions or possible evacuations, reducing the uncertainty surrounding each episode of anomalous activity.
A project that opens up new scientific questions
As is often the case in science, the work doesn't end with the publication of the first image. Although the 3D tomography of Popocatépetl has contributed important certainties —such as the identification of multiple reservoirs and the concentration of magma towards the southeast—, has also generated new unknowns that the team wants to address in the coming years.
Among the open questions, the need to to understand why seismicity is more intense in certain areas from the interior and what implications this has for the volcano's future evolution. Questions are also raised about how these patterns might change if the system experiences an additional injection of magma from greater depths or if the connectivity between magma chambers is altered.
To answer these questions, researchers are considering the possibility of repeat measurement campaigns and periodically update the three-dimensional model, which would allow Popocatépetl to become a true "natural laboratory" in the long term. Combining seismic data with other techniques, such as satellite-measured deformation or detailed gas analysis, could further refine the understanding of what is happening beneath the surface.
The team also emphasizes the educational value of these types of projects. Young researchers like Karina Rodriguez They have found in Popocatépetl a testing ground where hard work in high mountains, the analysis of complex data, and direct involvement in a public safety issue are combined. That experience, they say, is one of the driving forces that motivates them to start new projects and keep climbing the volcano.
After years of ascents, nights at the foot of the crater, and thousands of hours processing signals on the computer, the image of the interior of Popocatépetl moving in 3D on the screen It has become the team's greatest reward. A visual representation that summarizes the collective effort and, at the same time, marks the starting point of a new stage in the study of one of the most closely monitored volcanoes in the world, with lessons that are already being closely observed by other volcanic observatories in Mexico, the Americas, and Europe.
