La Mexico's recent history is marked by volcanoes and earthquakes that have forever marked the collective memory. On the night of March 28, 1982, the Chichón volcanoIn Chiapas, the volcano awoke after centuries of apparent calm and devastated entire Zoque communities in a matter of hours. That lethal eruption, with more than two thousand victims and villages buried under ash and rocks, made it clear that beneath our feet lies a geological system far more active than we usually imagine.
This extreme scenario is not an isolated anomaly, but rather the visible face of a deep network where tectonic plates, faults, and magma chambers converge. An essential part of this mechanism is the Trans-Mexican Volcanic Belt The Trans-Mexican Volcanic Belt (TMVB), also known as the Trans-Mexican Volcanic Belt, is a strip of land that crosses the country from ocean to ocean and is home to a large percentage of the population. Understanding what it is, how it formed, and what risks it entails is not a matter of morbid curiosity, but a fundamental piece of scientific literacy for anyone living in Mexico.
What is the Trans-Mexican Volcanic Belt?
El The Trans-Mexican Volcanic Belt is a tectono-volcanic province that crosses the central portion of the country from the Pacific to the vicinity of the Gulf of Mexico. In satellite images it is distinguished as a band of volcanic relief approximately 900-1.000 kilometers long, roughly stretching from the Banderas Bay area (Jalisco-Nayarit) to eastern Veracruz, near Punta Delgada.
In a north-south direction, the width of the CVT varies considerablyIn its central section, roughly between San Luis Potosí and northern Morelos, the volcanic belt reaches a width of about 400 kilometers, while to the east, between the Teziutlán region (Puebla) and the city of Orizaba (Veracruz), it narrows to about 100 kilometers. This irregular geometry is due to a mosaic of blocks, faults, and stepped basins that influence both the topography and seismic activity.
Some of the Major Mexican metropolitan areas: Mexico City, Puebla, Guadalajara, Toluca, or TlaxcalaAmong many others. Various studies estimate that around 40% of the national population—and some analyses even suggest 50% or more—lives within the active zone of the Trans-Mexican Volcanic Belt. This makes the Trans-Mexican Volcanic Belt one of the regions on the planet where the interaction between geological processes and human density is most intense.
The CVT is located emblematic volcanoes such as Popocatépetl, the Colima volcano, Pico de Orizaba, Nevado de Toluca or ParicutínThese are joined by thousands of monogenetic volcanic structures—small cones that record only one eruption throughout their life—as well as lesser-known calderas and volcanic fields, which are equally important from a geological and risk perspective.
An old system, still in motion
The Trans-Mexican Volcanic Belt It is not simply a geological relic of the pastIts history begins at least several million years ago, with intense volcanic activity during the Plio-Quaternary period (approximately from 5 million years ago to the present). However, stratigraphic and geochronological studies show that volcanism existed in some areas prior to the Oligocene and Miocene epochs, that is, more than 20-30 million years ago.
Under the CVT, the following have been identified two major stages of volcanismThe first phase occurred during the Oligocene-Miocene, and the second during the Pliocene-Quaternary, separated by intervals of relative inactivity that are not identical throughout the belt. In areas such as Los Humeros (Michoacán) or the Caldera de la Primavera region (Jalisco), a cessation of activity is observed followed by a subsequent reactivation, with pauses that can exceed two or three million years, but which vary greatly from one sector to another.
This intermittent behavior has left a complex sequence of lavas, tuffs, pyroclasts and sedimentsinterbedded with one another. The large basins of the CVT—such as those of Toluca, Mexico, Puebla-Tlaxcala, the Oriental or the Colima Basin—are filled with lacustrine, alluvial and fluvial sediments, intermixed with volcanic products of different mineralogical and chemical composition, deposited in different eruptive episodes.
The current landscape reflects that history: a region in the process of emergence, affected by tensional forces that generate tectonic rifts and elevated pillarsTo the west, for example, in Nayarit and Colima, the basins can be located at about 400 meters above sea level, while towards the central-east, as in Toluca or Tlaxcala, the altitudes exceed 2.600 meters. This stepped arrangement is the result of a crustal uplift dotted with fractures and faults that are still active.
Taken together, the structural and paleomagnetic data indicate that the The Trans-Mexican Volcanic Belt behaves as a single tectonic domainwithout large-scale, independent block rotations on a regional scale. The deformation is best explained by a transtensional regime, where extension dominates over lateral shear, although the latter is also present.
How it formed: plates that don't quite fit together
The peculiarity of the CVT lies in the It does not follow the typical geometry of a classic volcanic arcAt many of the planet's subduction zones, volcanic chains run roughly parallel to the oceanic trench where one plate sinks beneath another. In Mexico, however, the volcanic belt cuts across that margin at an oblique angle. It's as if two rows of cars collided head-on, but offset laterally: the impacts are not evenly distributed, nor do they all occur simultaneously.
The key lies in the interaction between the Cocos and Rivera oceanic plates, which subduct beneath the North American plateand to a lesser extent, the influence of the Caribbean Plate. These plates do not subduct at the same rate or angle along the Mexican coast. The tilt angles of the Cocos Plate, for example, vary between about 20° and more than 40° depending on the region, and its relative displacement is around 23 millimeters per year in some areas, accelerating in others towards the southeast.
The variations in the age, thickness, and angle of subduction of the plates These factors influence the depth at which magmas are generated, their composition (ranging from andesites to dacites and rhyolites, as well as more basic magmas), and where they emerge at the surface. This results in a mosaic of volcanoes with distinct characteristics along the belt and an apparent migration of eruptive centers over time.
Some models propose that the CVT can be interpreted as a intracontinental volcanic arc associated with a crustal fissureThe belt was opened by the assimilation of the Cocos Plate beneath the continent. Others have suggested that it is the reactivation of an ancient rift in the continental basement or the continental continuation of a mid-ocean ridge that had already been absorbed. In any case, the evidence agrees that the combined dynamics of the North American, Cocos, Rivera, and Caribbean plates have been decisive in the origin and evolution of the belt.
An illustrative example is the Banderas Bay region, where the The subduction of the Rivera Plate would have acted as a wedgeThis process favored crustal rupture and the formation of highly complex fault and graben structures (sunken valleys) such as the Chapala and Cuitzeo areas. This interplay of sunken and uplifted blocks extends inland, giving rise to the large volcanic basins of central Mexico.
Seismicity, slow deformations and a subsoil that “breathes”
The Trans-Mexican Volcanic Belt is part of the Pacific Ring of FireThe Central Valley, a tectonic zone, accounts for approximately 90% of global seismic activity and around 75% of the planet's active volcanoes. While we often associate major Mexican earthquakes with the Pacific coast, the country's interior also experiences significant seismicity linked to the Central Valley.
Along the belt, there have been historically significant earthquakessuch as the Acambay earthquake of 1912 or other events in the 20th and 21st centuries, including those in Michoacán. Many of these earthquakes originate in internal fault systems, far from the coastline, and their danger lies in their proximity to densely populated urban centers.
In recent decades, research by the Institute of Geophysics at UNAM and other groups has focused on more subtle phenomena, such as slow seismic eventsThese are landslides that occur in subduction zones over weeks or months, releasing energy gradually and practically imperceptibly to the population. These processes have been particularly studied in Guerrero and Oaxaca.
Thanks to geodetic and seismic monitoring networks, it has been observed that these events cause crustal deformations on the order of 10 to 15 millimetersIt's a kind of slow breathing of the subsoil that, although not felt like a classic earthquake, can influence the accumulation of stress and the buildup of larger earthquakes over time. This "silent seismicity" forces us to rethink how active faults are monitored and what indicators should be integrated into early warning systems.
Specialists emphasize that Earthquakes and volcanoes are different manifestations of the same tectonic context.However, they do not follow a simple cause-and-effect relationship. The continuous subduction zone generates, on the one hand, persistent seismicity, especially along the coast, and on the other, an active volcanic axis that runs through the country. The interaction between these two processes is complex and still the subject of intense research.
Iconic volcanoes and natural laboratories
Among the many volcanic features of the CVT, some have become veritable open-air laboratories for volcanology. The case of the Chichón volcano, although not located exactly within the belt but in the Chiapas volcanic arc, shares the same tectonic context of subduction and has been fundamental to understanding how these systems respond after a large eruption.
Since the 1982 catastrophe, the Chichón has alternated long periods of relative calm with phases of reactivationFor many years, monitoring was incomplete or discontinuous, with seismic networks operating precariously or intermittently. Much of the change was detected almost "by hand," through direct observation by those who lived or worked in the area.
In recent times, institutions such as Cenapred and UNAM have strengthened surveillance, incorporating measurements of gas chemistry, crater lake observation and denser seismic networks. For example, a notable change in the lake's color has been documented: from a greenish hue, dominated by algae, it has shifted to a grayish turquoise associated with silicas and sulfates. New fumaroles with yellow sulfur deposits have also appeared, and the highest levels of hydrogen sulfide ever measured have been recorded, with increases of up to two orders of magnitude between 2021 and 2025.
As of June 2025, a [unclear] has been identified under the Chichón building persistent seismic swarmwith episodes exceeding 100 earthquakes per day. All of this indicates a clear change in the state of the volcanic system, interpreted as a reactivation phase. However, the scientific community insists that these signs do not equate to an imminent eruption, but rather to the need to maintain and improve monitoring in order to react promptly to any developments.
Other volcanoes in the CVT, such as Popocatépetl or the Colima volcano, are objects of continuous monitoring and multiple lines of researchIn the case of Colima, for example, artificial intelligence algorithms have already been tested to reanalyze seismic series and detect non-evident patterns, allowing for a more precise identification of precursor signals of changes in activity.
Volcanic risks: much more than lava and fire
When we talk about volcanoes, the image that usually comes to mind is... spectacular eruptions with columns of ash and rivers of lavaHowever, the risk associated with the Trans-Mexican Volcanic Belt is much more diverse and, to a large extent, more insidious. One of the most recurring hazards is the fall of fine ash, which can affect respiratory health, contaminate drinking water sources, damage crops, and cause lightweight roofs to collapse.
In episodes of activity at Popocatépetl, for example, we have seen airports partially paralyzed And cities like Puebla or even Mexico City itself are covered by a thin layer of ash. Added to this are lahars, mixtures of water, mud, and rock fragments that can descend the slopes at high speed after heavy rains or sudden snowmelt, devastating everything in their path.
Pyroclastic flows—burning clouds of gas and fragmented material that travel at speeds of tens or hundreds of kilometers per hour—are less frequent, but extraordinarily destructiveAn eruption like that of Chichón in 1982 or the historic ones of Colima or Popocatépetl demonstrate that these phenomena can bury entire communities in a matter of minutes.
Added to this are the monogenetic volcanoes of the CVTSmall cones that are born, erupt, and disappear in relatively short periods. Paricutín, which emerged in 1943 in a farmland in Michoacán, is the classic example: in just a few years, it radically transformed the local landscape. The current concern is that similar phenomena could occur in areas that are now highly urbanized, which would imply conflicts between land use, infrastructure, and new eruptive centers.
The real challenge of the belt is not only geological, but demographic and territorial: More than half of the Mexican population could reside in this active zoneover ancient volcanic basins and soils that in many cases amplify seismic waves. Any event of moderate or high magnitude has the potential for enormous impact on buildings, roads, utility networks, and critical structures.
Monitoring, science and artificial intelligence: measuring what cannot be seen
Monitoring a system as complex as the CVT requires seismic, geodetic, geochemical and volcanic monitoring networks operating continuously. In recent decades, Mexico has made significant progress in this field, especially through institutions such as Cenapred, UNAM, and other research centers. Even so, notable budget and infrastructure shortcomings persist.
In many volcanoes, the instrumental record shows temporary gaps, out-of-service stations or insufficient coverageThis limits the ability to detect subtle changes in time and hinders the full use of emerging tools like artificial intelligence. AI can help reanalyze large seismic databases, identify patterns preceding changes in activity, or automatically classify complex signals, but its effectiveness depends on having abundant, high-quality data.
In more robustly monitored sites, such as the Colima volcano, data has already been obtained promising results applying machine learning algorithms to distinguish between different types of seismic events and improve early warning. However, in other systems, such as El Chichón, the historical discontinuity of data first necessitates consolidating the instrumental networks before aspiring to truly operational AI-based monitoring.
In addition to instrumentation, basic science plays a crucial role. Paleomagnetic studies across the entire Trans-Mexican Volcanic Belt (TMVB), with hundreds of samples of Miocene-Recent lavas, have allowed reconstruct the history of the geomagnetic fieldto verify the absence of large block rotations and estimate migration rates of volcanic activity. In places like the Sierra de las Cruces, an apparent displacement of eruptive centers towards the southeast has been calculated, with rates between 1,6 cm/year and up to 4 cm/year at certain intervals.
These studies have also shown that the Geomagnetic field dispersion recorded in the rocks of the CVT Within the uncertainties, this coincides with global models for its latitude. Therefore, no anomalous "window for the dipolar field" is observed in Mexico, as some previous studies had suggested. All of this reinforces the idea that the belt behaves coherently from a tectonic and geomagnetic point of view.
Social and political dimension of risk
Beyond science, the Trans-Mexican Volcanic Belt poses a a profoundly political and social challengeRisk management depends not only on what is known in laboratories, but also on how that information is funded, organized, and communicated. In the case of El Chichón, for example, much of the current monitoring is sustained by university projects and efforts, without a stable and sufficient budget allocation from the State.
This reality complicates the consolidation of robust, long-term surveillance networks. At the same time, progress has been made in recent years in link between authorities, scientists and local communitiesIn Chiapas, there were communities that did not even appear in the official evacuation plans; they were known thanks to visits from volcanologists, but were absent from civil protection maps.
Since 2020, Civil Protection has made a concerted effort to incorporate these “invisible” localities through field visits, participatory mapping, and the creation of community humanitarian committees. These groups receive training in risk management, evacuation protocols, and communication with authorities, which strengthens the collective response to potential emergencies.
In parallel, emphasis has been placed on the importance of sensory detection of changes by the populationUnusual sulfur smells, changes in water color, the appearance of new fumaroles, or strange underground noises are all signs of potential problems. The recommendation is clear: don't panic, but do report any anomalies to official channels and follow information from verified sources. People who live near volcanoes are, ultimately, the first line of observation.
All of this suggests that the risk of CVT is not just a matter of geodynamics; it is also a matter of urban planning, resilient infrastructure and sustainable public policiesBuilding in seismic and volcanic zones without strict regulations, without adequate building standards and without education in prevention multiplies vulnerability to phenomena that, in themselves, cannot be avoided.
The Trans-Mexican Volcanic Belt is, at the same time, a source of soil fertility, water resources and iconic landscapesAnd a constant reminder that Mexican territory is in perpetual transformation. Its volcanoes, faults, and slow deformations are not museum pieces, but active processes that will continue to influence the lives of millions of people. The better we understand this intricate web—from the microscopic scale of magnetic minerals to the human scale of communities at risk—the greater our capacity to coexist with a country that, quite literally, never stops moving.
