Volcano that killed thousands shows frightening new activity underground

Chichón warrants attention, though not alarm.Between June and December 2025, scientists from the National Autonomous University of Mexico (UNAM) documented several physical and chemical shifts within the volcano’s crater system.

Their findings come decades after the 1982 eruption that killed at least 1,900 people and destroyed nine villages.Volcanologist Erik Klemetti has previously described the 1982 blast as “one of the most important volcanic events of the 20th century.” He noted: “The eruption of El Chichón is overlooked in comparison to other historic eruptions like Mount St Helens in 1980 or the Pinatubo eruption in 1991, yet it teaches us a number of important lessons about how we can be better prepared for volcanic disasters and the potential influence of volcanoes on the Earth’s climate.

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What researchers observed in 2025

According to UNAM’s monitoring team, the most visible shift occurred in the crater lake. Typically green and rich in algae, the water has turned grayish, a change scientists say may reflect higher concentrations of sulfate and silica linked to evolving underground fluid circulation.Thermal readings also showed elevated temperatures along the lake bed and sections of the crater floor, rising above background levels normally recorded at the site.

Gas measurements detected accumulations of hydrogen sulfide and carbon dioxide near the crater. While both gases can pose risks in high concentrations, researchers emphasized that such emissions are common in hydrothermal systems. What drew attention this time was the increase compared to previous readings. Another unusual feature: small sulfur spheres forming in liquid sulfur pools close to the crater, an anomaly now under observation.

Is an eruption coming?

Despite the changes, UNAM volcanologist Dr Patricia Jácome Paz said the data do not point to magma rising toward the surface.Rather than indicating “fresh magma,” she explained that “the observed behavior is consistent with hydrothermal processes or minor steam-driven explosions.” She added that the activity is likely linked to superheated groundwater interacting with hot rock beneath the crater. In other words, the shifts appear tied to the volcano’s hydrothermal system, not necessarily to an impending eruption.UNAM’s report noted that the Chiapas Civil Protection Secretariat remains in regular contact with nearby communities, including local tour guides, to reinforce safety protocols and provide clear information about volcanic hazards. For now, experts describe the situation as one that requires vigilance, not panic. But given El Chichón’s history, and the scale of devastation in 1982, even subtle internal changes are enough to keep scientists watching closely.