Volcanic influence on sediment dynamics and flow distribution at the Mezcalapa River bifurcation, southeast Mexico

Influencia volcánica en la dinámica sedimentaria y la distribución del flujo en la bifurcación del río Mezcalapa, sureste de México

Alejandro Mendoza1, Fabian Rivera-Trejo2,*, Gastón Priego-Hernández3, Moisés Berezowsky1 

1 Instituto de Ingeniería, Universidad Nacional Autónoma de México. Circuito Escolar S/N, Ciudad Universitaria, Coyoacán, 04510 CDMX, México.

2 División Académica de Ingeniería y Arquitectura, Universidad Juárez Autónoma de Tabasco. Carretera Cunduacán-Jalpa km. 1, Col. La Esmeralda, 86690, Cunduacán, Tabasco, México.

3 División Académica de Ciencias Básicas, Universidad Juárez Autónoma de Tabasco. Carretera Cunduacán-Jalpa km. 1, Col. La Esmeralda, 86690, Cunduacán, Tabasco, México.

* Corresponding author: (F. Rivera-Trejo) This email address is being protected from spambots. You need JavaScript enabled to view it. 

How to cite this article:

Mendoza, A., Rivera-Trejo, F., Priego-Henández, G., & Berezowsky, M. (2026). Volcanic influence on sediment dynamics and flow distribution at the Mezcalapa River bifurcation, southeast Mexico. Boletín de la Sociedad Geológica Mexicana, 78(1), A150126. https://doi.org/10.18268/BSGM2026v78n1A150126 

Manuscript received: July 4, 2025. Corrected manuscript received: November 7,2025. Manuscript accepted: November 25, 2025.

ABSTRACT

The 1982 eruption of El Chichón volcano, one of the most destructive volcanic events of the 20th century in Latin America, ejected large volumes of pyroclastic material into the Mezcalapa River catchment, located in southeastern Mexico. Approximately 75 km downstream from the location of the volcano, the Mezcalapa River bifurcates into the Samaria and Carrizal rivers, which supply water to highly populated and agriculturally important areas in Tabasco state. This bifurcation is a key fluvial characteristic and variations in its f low distribution have historically caused significant social and economic impacts due to f looding and infrastructure stress. Around one year after the eruption, the bifurcation’s f low distribution started a new trend, where the dominant branch began gradually to capture less f low, reversing the trend observed in the preceding decades. This study investigates how and whether a volcanic eruption influences sediment dynamics and hydromorphological processes that could explain this shift. First, historical records and field measurements were analyzed to assess post-eruption changes in sediment load. Second, a morpho-hydraulic numerical model was applied to evaluate the effects of variations in sediment supply on the bed morphology and f low distribution of the bifurcation. Results show that suspended sediment loads increased by a factor of 3 to 10 after the eruption. Even 32 years later, the Platanar River still exhibited sediment concentrations twice as high as pre-eruption values. Modeling revealed that increased sediment supply may modulate differential erosion and sedimentation processes in the branches of the bifurcation, and it can modify the f low distribution. These findings underscore the long-term impact of volcanic eruptions on sediment transport and river morphology. They highlight the need to integrate volcanic sediment dynamics into fluvial hazard assessments and the importance of monitoring and modelling strategies to anticipate downstream consequences in sediment-sensitive elements of fluvial systems such as the Mezcalapa bifurcation.

Keywords: river bifurcation, flow distribution, volcanic impacts, sediment dynamics, geophysical hazards.