Geohistory and geomorphology of the Mitlatongo landslide, Oaxaca, Mexico

Abstract

When a landslide occurs, the landscape is radically transformed; a pristine, unexplored geography emerges, with new morphogenetic processes. When the event also affects human settlements, it is crucial to understand all the physical and geographic factors that explain it and all its multiple social implications. In September 2011, a landslide occurred in the Mitlatongo Valley, rendering more than 400 homes unusable and forcing the displacement of more than 1,500 people living there. The trigger was intense and prolonged rains that saturated the soil in a geologically unstable area. Despite the significance of the event, very little documentation is available. This information is not only limited to the landslide but also to the historical background of Mitlatongo, as it is a settlement with pre-Hispanic origins. For this reason, this work presents a geohistorical analysis based on a detailed geomorphological and geological map, which documents the transformations of the landscape before and after the disaster. To this end, the study integrates multiple sources of information (historical aerial photographs, archival documentation, local testimonies, and drone photogrammetry), processed and analyzed using GIS to reconstruct the geomorphological dynamics before and after the event. The geomorphological map reveals the complexity of the landslide, distinguishing three sectors: scarp areas, accumulation zones, and pre-existing fractures. Five main units were identified within the landslide, with ground displacements of up to 225 meters. Geological mapping highlights the interaction between tectonic structures, such as the Tres Lagunas-Santa Cruz fault and the Pueblo Viejo syncline, and the processes of erosion and soil saturation. Taken together, they provide a comprehensive perspective on the event and its impact on ground dynamics. This paper also highlights the social impact of the landslide, which resulted in an ineffective government response, leaving the community in precarious conditions.