Mariana Sandoval García

The spatial and temporal transition from polygenetic to monogenetic volcanism was studied in a 15 km ² area of southwestern Mexico City using Sentinel-1 SAR imagery (10 m), a 5 m LiDAR DEM, and geological mapping. Nineteen volcanic structures were identified: two dacitic polygenetic dome complexes (Ajusco and Los Picachos, ~ 3 Ma), ten intermediate-aged domes (1.6–0.18 Ma) and five younger monogenetic scoria cones, a fissure and a dike (~ 28–25.1 ka). Seven domes and one cone were previously unrecognized. New ⁴⁰ Ar/ ³⁹ Ar ages, from whole rock and groundmass, were obtained for the domes Ojo (1.624 ± 0.088 Ma), Cañada 1 (1.35 ± 0.12 Ma), and Cerro El Judío (1.328 ± 0.26 Ma), while relative ages of the other domes and scoria cones were estimated by stratigraphy and morphometry. Older polygenetic domes formed along N65°W-trending faults under compressional–transtensional stress, whereas younger scoria cones were emplaced within N65°W and E45°W-trending grabens under transtension. Intermediate domes extruded along N65°W grabens trending under lower stress. Geochemical analyses of 25 samples (domes, cones, flows) show that scoria cones cluster into distinct groups with higher Mg#, while domes exhibit lower Mg#. Although volumetrically similar to scoria cones, intermediate-aged domes share geochemical traits with polygenetic volcanoes, reflecting longer magma residence. The Lobos cone and the dike are geochemically similar to older volcanoes, whereas the Ojo and Roto domes align geochemically with scoria cones, suggesting deeper sources influenced by tectonic controls. Polygenetic volcanoes, intermediate domes, and scoria cones developed under different structural and magmatic regimes. Intermediate-aged domes mark the transition between long-lived polygenetic volcanism and short-lived monogenetic cones.

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.

The transition and coexistence of large polygenetic volcanoes and monogenetic volcanic fields represents a key challenge in understanding crustal magmatism and volcanic evolution across active tectonic regions worldwide. This duality is strikingly exemplified in central Mexico. Here, the active polygenetic volcano Popocatépetl, coexists with the Chichinautzin Monogenetic Volcanic Field (CMVF), characterized by numerous small cones and lava flows reflecting short-lived, episodic eruptions. Although both volcanic styles are extensively documented individually, the fundamental tectonic and structural factors controlling their coexistence and transtition remain poorly understood. Our study aims to understand the influence of regional tectonic stress orientation and local faulting in interpreting the mechanisms that governs eruptive style transitions.We integrated high-resolution structural mapping, remote sensing, and a 30-year seismic record (1994–2025). Fault and lineament patterns were derived from LiDAR Digital Elevation Models (DEMs) and Sentinel-1 SAR imagery, processed through slope, azimuthal, and contour analyses. These datasets were correlated with volcanotectonic (VT) earthquake records from Popocatépetl and CMVF to assess the spatial and temporal distribution of seismicity in relation to fault systems.Our results delineate two major tectonic domains: (1) NW–SE and NE–SW fault systems characterizing the Popocatépetl volcano; and (2) a predominant E–W system defining cone alignments within the CMVF. Monogenetic cones in the CMVF align preferentially along E–W and NE–SW faults, reflecting a prevailing N–S minimum horizontal stress that facilitates direct magma ascent. In contrast, Popocatépetl is dissected by multiple, interacting, high-angle fault systems, including the active Tlamacas (NE–SW) and Nexpayantla (NW–SE) faults. The majority of pre-eruptive and co-eruptive VT earthquakes cluster along these structures, confirming their critical role in magma ascent, storage, and edifice segmentation.We conclude that the coexistence and transition between polygenetic and monogenetic volcanism in central Mexico are fundamentally governed by the complexity and orientation of regional and local stress fields. In the CMVF, single stress regimes create efficient pathways for rapid magma ascent, favoring monogenetic activity. At Popocatépetl, intersecting and structurally complex fault systems induce magma trapping and long-term storage, driving polygenetic evolution.

La topografía prexistente jugó un papel fundamental en definir la trayectoria de los derrames de lava del Xitle. El Xitle es de los volcanes monogenéticos más jóvenes del sur de la Ciudad de México. Su erupción se caracterizó por emisiones menores de ceniza y de nueve derrames de lava pahoehoe y aa que cubrieron 78.94 km2. En este trabajo se reconstruyó el paleo-relieve del área del volcán Xitle para mejorar el conocimiento del pa- leo-drenaje y cómo determinó la trayectoria de los derrames de lava y la formación de tubos de lava. Se identificaron los depósitos de los volcanes pre-Xitle (Complejo Volcánico San Miguel, Ajusco, Cuilotepec, Coatzontle, Yololica y Malinale) según la morfología del relieve actual. Se modificaron las curvas de nivel del relieve actual para eliminar la topografía de los derrames de lava del Xitle y mediante la creación de una superficie ráster a partir de un TIN, se obtuvo un modelo digital de elevación del paleo-relieve. La distribución de los paleo-ríos se definió mediante el análisis de la acumulación y dirección de flujo en el paleo-relieve. Los derrames de lava del Xitle se simularon individualmente en el paleo-relieve con el programa probabilístico Q-LavHA. Se integraron las observaciones hechas en campo y estudios previos del volcán Xitle para definir los parámetros de las simulaciones de los derrames. Los derrames de lava del volcán Xitle cubrieron los depósitos de los volcanes pre-Xitle con excepción de las partes más altas como el caso del cono del volcán Cuilotepec y los montículos (hummocks) del Ajusco. Las lavas modificaron los cauces de algunos paleo-ríos (e.g. Magdalena) y rellenaron por completo otros (e.g. Cuicuilco). Las simulaciones muestran que las trayectorias de los derrames y la existencia y distribución de los tubos de lava están asociados a variaciones en la tasa de efusión, la disposición de los paleo-ríos, la morfología de los depósitos pre-Xitle y la abrupta pendiente del paleo-relieve.