Precursors to Tephra Emission, Variation and Dispersal at Popocatepetl Volcano (Mexico), 2023-2026

Nearly 20 million people live within a100 km radius from Popocatepetl volcano in central. Mexico. Ashfall is frequent since emissions began in 1994. Ash is sampled weekly or daily depending on the activity. A 200 site ash monitoring network is enhanced by community participation and reports. Negative magnetic anomalies (WD 5nT) during March and April 2023, September 2024 and during the first 4 days in April 2025 were correlated with harmonic tremor and small chemical changes in the springwater near the volcano. These precursors preceded abundant ash emission in 2023 and 2024 by 2 month and small ash emissions in 2025 and 2026. This allowed us to advice Civil Protection weeks before and get the population prepared with facemasks and get school protocols into place. The Mexico City and Puebla international airports were closed for 2 days in 2023 and bad road visibility due to the fine ash caused serious transportation problems. Crops were also affected but only minor respiratory health problems occurred. Ash composition varied from 58- 60 SiO2 % in 2023 and from 59 -61 SiO2 % in 2024. Smaller amounts of ash in 2025 and 2026 are associated with the formation of small lava domes while the larger emissions result from a constant ash emission over several days.