UNAM scientists detect hydrothermal unrest in El Chichón volcano crater lake, Mexico

Key facts

• El Chichón volcano is located in northern Chiapas state, Mexico.
• The National Autonomous University of Mexico (UNAM) researchers reported physical and chemical changes in the 1-km-diameter, 200-m-deep crater lake formed after the 1982 eruption.
• The 1982 eruption caused over $117 million in damage and displaced local populations.
• Lake water, historically sulphur-rich and near 100 °C, now shows heightened sulphate and silica content and changed colour due to reduced algal influence.
• Hollow sulphur spheres floating on the lake indicate a bottom layer of liquid sulphur where temperatures reach 118 °C.
• Between June and August 2025 seismic activity increased, prompting investigations by several institutions.
• Current activity is hydrothermal with possible minor phreatic explosions; no evidence of ascending fresh magma, so a repeat of the 1982 eruption is considered unlikely.