Reducing volcanic risk through joint efforts of academia and key decision-makers, with the geochemical monitoring of volcanic activity

Millions of people worldwide are exposed to hazards associated with volcanic activity. Currently, in México, around dozens of volcanoes pose different levels of risk to the surrounding population. Various monitoring methods have been employed at the highest-risk volcanoes, most of which rely on seismological and geodetic surveillance. However, the complexity of volcanic activity requires additional methods, among them the follow-up of the chemistry of volcanic products, such as gases and tephra, as well as their secondary effects, mainly their interactions with water bodies in or near volcanic edifices. To that aim, joint efforts have been developed for more than 30 years between the Geophysics Institute of the National Autonomous University of Mexico and the National Center for Disaster Prevention. These methods have included the sampling and chemical analysis of water from springs, wells, and lakes from Popocatépetl, Ceboruco, Nevado de Toluca, Pico de Orizaba, San Martín Tuxtla, El Chichón, and Tacaná volcanoes, and tephra leachates from Popocatépetl volcano, followed by the interpretation of their analyses in terms of their implications in the context of volcanic risk.  Important changes have been observed in the chemistry of the 7 springs around Popocatépetl volcano sampled since 1995, such as the finding of boron above its detection limit in one of them before the emplacement of the first lava dome in March 1996, and the increase of dissolved CO₂ and boron in all of them about 5 months before the fast growth of the largest dome recorded in the current period of activity in December 2000, that was followed by its destruction by intense explosions in January 2001. This episode, along with other signals of unrest, was a primary factor in the decision of the Civil Protection Authorities to evacuate over 40,000 inhabitants from the area around the volcanic edifice. The chemistry of Popocatépetl ash leachates has also shown changes related to fluctuations in volcanic activity, mainly an increase in the Cl/F ratio and changes in the SO4, Cl, and F relations associated with phreatic and magmatic eruptions. The chemistry of springs at Ceboruco, San Martín Tuxtla, and Pico de Orizaba has been stable for a decade, while the crater lake waters of Nevado de Toluca and El Chichón have shown important differences reflecting the quiet state of the former and the influence of an active geothermal volcanic system in the latter. Recent changes at El Chichón have also prompted the authorities to take preventive actions involving the population to enhance their awareness and resilience to the hazard posed by that volcano.