Popocatépetl, often nicknamed “El Popo,” is one of the world’s most monitored and active volcanoes, standing as a prominent geological feature in central Mexico. Its immense, snow-capped cone is visible from Mexico City, located only about 70 kilometers away, placing millions of people within its potential impact zone. The question of when the volcano last erupted is complex because the mountain exists in a near-constant state of restlessness. For volcanologists, defining the “last eruption” means distinguishing between the daily release of gases and ash and a major, significant eruptive phase that requires civil protection measures and public alerts.
Popocatépetl’s Recent Eruption History
Popocatépetl reawakened in December 1994, marking its first significant activity after approximately 70 years of quiet. This event began the current period of continuous unrest, involving the emission of ash and sulfur-dioxide, and prompting the temporary evacuation of thousands of residents. Since then, the volcano’s behavior has been characterized by episodes of lava dome growth within the summit crater, followed by explosions that destroy the dome and expel ash and incandescent rock fragments.
A major eruptive pulse occurred in December 2000, described by scientists as the volcano’s largest display in 1,200 years, necessitating the evacuation of tens of thousands of people. The most recent continuous eruptive period began in January 2005 and is still ongoing. This period is defined by near-daily episodes of seismic tremors, gas-and-ash emissions, and explosions, including a notable event on December 25, 2005, which ejected an ash column three kilometers high.
More recently, activity has included significant ash plumes reaching altitudes of up to 9.7 kilometers in May 2023. The daily activity typically consists of low-intensity exhalations of water vapor, volcanic gases, and light ash, along with periods of harmonic and high-frequency tremor. Consequently, the volcano is not considered to have a single “last eruption” date but is viewed as being in an extended, active eruptive sequence that has persisted for decades.
Geographical Context and Volcanic Type
Popocatépetl is a giant stratovolcano, characterized by its steep-sided, symmetrical cone built up by layers of hardened lava and ash. At 5,426 meters, it is the second-highest peak in Mexico and forms part of the Sierra Nevada range. Its location within the Trans-Mexican Volcanic Belt (TMVB) is the primary reason for its activity.
The TMVB is an active continental volcanic arc that stretches east-west across central Mexico. This activity is driven by the subduction of the Cocos Plate beneath the North American Plate. As the oceanic crust sinks and is heated, it releases water that lowers the melting point of the overlying mantle rock, generating magma.
The viscous nature of the andesitic and dacitic magma associated with stratovolcanoes contributes to Popocatépetl’s explosive eruption style. This magma traps volcanic gases, causing immense pressure to build until it is released in violent explosions. This geological setting explains why the volcano poses a constant threat, as these eruptions can produce pyroclastic flows and lahars, which are destructive volcanic mudflows that travel rapidly down the slopes.
Current Activity and Monitoring Status
The ongoing activity of Popocatépetl is subject to intense scrutiny by Mexico’s National Center for Disaster Prevention (CENAPRED). This agency coordinates monitoring efforts, including seismic networks, gas emissions measurements, and satellite imagery. The primary tool for communicating risk is the Volcanic Traffic Light System, known as the Semáforo de Alerta Volcánica, which uses a three-color scale to indicate the volcano’s status.
The alert level is frequently maintained at Yellow Phase 2, which signifies increased activity including minor to moderate explosions, variable-amplitude tremor, and light ashfall. This phase also anticipates the possibility of incandescent fragments being expelled near the crater. A change to the Red alert level would signal an imminent major eruption, triggering evacuation protocols.
As a safety measure, authorities maintain an exclusion zone that typically extends 12 kilometers from the crater. Adhering to this boundary protects against ballistic projectiles and sudden pyroclastic flows. The continuous monitoring and alert system track even daily low-intensity emissions of steam, gas, and ash, providing essential data for assessing the volcano’s internal state and potential for escalation.