Geophysical characterization and hazard zoning for mass wasting on the slopes between km 21 and 23 of the Zanjón-Pueblo Bello Road, Cesar

Abstract

This manuscript presents a slope landslide hazard analysis using deterministic and heuristic techniques at a 1:5000 scale in the section between Km 21 and Km 23 of the Zanjón-Pueblo Bello road. The study identifies the predominant geological units, analyzes their geotechnical properties, and determines the relevant geomorphological elements. These analyses are complemented by geophysical studies using Electrical Resistivity Tomography (ERT) to obtain subsurface information on different soil types through resistivity data and to locate the water table. The exposed slope materials
primarily consist of fine to coarse sand (A-3), mineralogically composed of quartz with small amounts
of kaolin-type clay. This clay is attributed to the alteration of feldspars within the quartz monzonite facies of the Pueblo Bello Batholith. Geotechnically, these materials exhibit low or no plasticity, facilitating water infiltration, increasing pore pressure, and reducing shear strength. Considering these conditioning and triggering factors, a mass-wasting hazard map was generated. The results indicate that 15% of the area presents a very high hazard, 60% a high hazard, 15% a medium hazard, 5% a low
hazard, and 5% a very low hazard. These findings confirm that the steep slopes and the presence of clay significantly contribute to the high hazard level, as their interaction with water leads to instability and potential landslides, which pose a threat to the communities in the region.