Geotechnical investigation and stability modeling of a fatal rock-toppling event at a tourist site in Brazil

In Geotourism-dependent regions, landslide-related disasters can significantly impact their socioeconomic foundations. An example is the rock-toppling event in a canyon at the Furnas reservoir in Brazil, which caused 10 fatalities. Tourist fear and its temporary closure severely impacted the economy of the surrounding municipalities. To support a safer operation of the canyon, our study investigates the factors that can lead to rock instabilities, based on field investigations, rock-mass quality evaluation and both kinematic and stability analyses. The stability analysis, based on FEM and LEM methods, indicates that the rock-toppling event was initiated by rainfall infiltration and overland-flow accumulation in the jointed bedrock, as well as by the influence of the rapid reservoir water level increase, which potentially altered pore-water pressure in the discontinuities. The long-term erosion at the base of the slope weakened rock-mass support and also contributed to the slope failure. The kinematic and structural analysis demonstrated that the areas that show a higher rock-toppling susceptibility are those where two perpendicularly oriented structural features intersect. The rock-mass quality evaluation further supported the identification of structural zones that are more prone to slope failure(s) and, as a consequence, should be monitored. Our results supported the establishment of visitation procedures and geohazards-management strategies in the canyon and contribute to the gap of studies about rainfall and its effects on slope stability in reservoir settings.