First Field Findings and their Geological Interpretations at the Study Site Bello Oriente, Medellín, Colombia (Project Inform@Risk)

The City of Medellín, Colombia, subject to the german-colombian project Inform@Risk, has suffered from multiple landslides in the recent past. Embedded in the Aburrá Valley in the Cordillera Central of the Andes, the region around the city consists of different triassic and cretaceous metamorphic rocks and magmatic batholites and plutonites. Especially the north-eastern slope is prone to landslides, as it is very steep and made up of a deep cover of soil over highly weathered dunite rock. During the first field trip, carried out in August 2019, former landslide areas were mapped and ERT-measurements were conducted at the study site Bello Oriente in the northeast of Medellín. After a first evaluation of the findings, the rock surface seems to be even deeper than expected, over 50 m in the middle of the slope, almost at the surface in the north and south of the study area. This indicates multiple faults and possibly also a deep-seated landslide, which might have been moving downhill very slowly for thousands of years. The more dangerous landslides however, which are much faster, are the shallow ones on the surface. These landslides can appear on top of each other and are distributed across the whole study area, but are most concentrated between and above the last houses of the barrio. All those findings are preliminary; The ERT-profiles have to be calibrated and complemented by drillings, the landslide map has to be completed and a geological map has to be created. A second field campaign in February/March 2020 will see to these tasks.