Controls over debris flow initiation in glacio-volcanic environments in the Southern Andes

Abstract. The southern Andes is an active zone of mass wasting processes. Several conditioning factors could have an impact on the generation of debris-flows, influencing by water storage and slope stability. We assessed the generation of the Ñisoleufu debris-flow, an active area of debris-flow generation, reviewing the interplay between geomorphological, geotechnical and hydrometeorological controls in debris flow dynamics. Our results highlight significant changes in soil moisture content on critical days associated with debris flow events. We revealed that the combination of areas with high water accumulation capacity from local runoff and slopes that capture precipitation effectively were crucial in the generation of debris-flows. Areas with granular volcanic soils acted as storage mediums for water, which, coupled with decreased shear strength, facilitated debris flow initiation. The thin and fine-grained layers of glacial deposits located beneath the volcanic soil, characterized by low hydraulic conductivity, created localized accumulation zones that reinforced the storage capacity of adjacent areas, particularly in pyroclastic volcanic deposits in the release zone. By understanding the combined effects of water accumulation, soil properties, and slope dynamics, this study contributes valuable insights into managing and mitigating debris-flow hazards in vulnerable regions.