Abstract

This study aims to characterize the grain size distribution of sediments in alluvial-colluvial deposits within the Copiapó River basin, Chile, to provide detailed information on their composition and enhance the understanding of debris flow behavior. Debris flows are mass-wasting events triggered by intense and localized rainfall, commonly occurring in the arid zones of the Coastal Range and the Andes. These flows are defined by their high density and a composition largely made up of gravel mixed with water, giving them non-Newtonian and viscoplastic fluid properties that enable the transport of large volumes of material. Grain size analysis revealed that the studied microcatchments contain sediments with low cohesion and high susceptibility to erosion, predominantly composed of angular and non-cohesive gravel and sand particles. These characteristics facilitate the initiation and mobilization of debris flows on steep slopes, which is typical of arid regions with high erosive energy. This research contributes to clarifying the relationship between sediment composition and debris flow dynamics, offering key granulometric data for the characterization of materials transported during mass movement events. © 2025, Universidade Federal do Rio Grande do Norte. All rights reserved.