Reconstructing 90 years of urban occupation and mass movement dynamics in Campos do Jordão (SP), Brazil: insights from ERT and FDEM methods

Campos do Jordão, a city situated in the Mantiqueira Mountains of São Paulo, Brazil, is highly susceptible to mass movements due to its steep topography and high annual precipitation. These hazards have been exacerbated by rapid urban expansion since the 1970s. This study investigates a critical slope sector in the Vila Abernéssia neighborhood, where a historical monastery constructed in the 1940s coexists with more recent infrastructure, including a school built at a lower elevation. In 2002, foundation works for the school triggered a landslide that severely affected both the construction site and the monastery's parking area. Despite subsequent stabilization efforts, signs of ground deformation, such as wall cracking and floor heaving, have persisted. To reconstruct the geomorphological evolution and subsurface conditions of the area, we integrated Electrical Resistivity Tomography (ERT), Frequency-Domain Electromagnetic (FDEM) surveys, geotechnical testing, historical and contemporary photographic records, and qualitative data obtained from local residents. The results reveal that slope instability has been driven by a combination of natural and anthropogenic factors, including heterogeneous landfill deposition, unregulated excavation, and hydrological influences. Two principal types of mass movement were identified: a shallow landslide and long-term soil creep, the latter likely sustained by ongoing loading and infiltration. The main novelty of this study lies in the reconstruction of nearly 90 years of slope evolution in a tropical urban environment through the integrated analysis of geophysical, geotechnical, historical, and community-based data. Rather than focusing on a single triggering event, the study demonstrates how successive anthropogenic interventions progressively modified subsurface conditions, ultimately leading to both rapid failure and long-term creep processes. This multidisciplinary approach enabled a detailed delineation of sliding surface geometries and highlighted how unplanned urbanization on geotechnically fragile terrain contributes to slope failure. The results provide a rare long-term perspective on the cumulative effects of urban occupation on slope stability in tropical environments, offering insights applicable to similar settings across the Global South. The site exemplifies broader patterns of development in Brazilian urban centers and similar contexts across the Global South, where inadequate land-use planning amplifies the risks posed by natural hazards.