Fustos et al. (2025) Controls over debris flow initiation in glacio-volcanic environments in the Southern Andes

Identification

• Journal: Natural hazards and earth system sciences
• Year: 2025
• Date: 2025-12-05
• Authors: Ivo Fustos, Daniel Basualto, Ardy Gatica, Alvaro Bravo-Alarcón, José Luis Palma, Gabriel Fuentealba, Sergio A. Sepúlveda
• DOI: 10.5194/nhess-25-4843-2025

Research Groups

• Departamento de Ingeniería en Obras Civiles, Facultad de Ingeniería y Ciencias, Universidad de La Frontera, Temuco, Chile
• Departamento de Ingeniería Eléctrica, Facultad de Ingeniería y Ciencias, Universidad de La Frontera, Temuco, Chile
• Programa de Magíster en Ciencias de La Ingeniería, Universidad de La Frontera, Temuco, Chile
• Departamento Ciencias de la Tierra, Facultad de Ciencias Químicas, Universidad de Concepción, Concepción, Chile
• Ministerio del Interior, Temuco, Chile
• Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile
• Department of Earth Sciences, Faculty of Science, Simon Fraser University, Burnaby, Canada

Short Summary

This study investigates the geomorphological, geotechnical, and hydrometeorological controls over debris flow initiation in glacio-volcanic environments of the Southern Andes, revealing that the combination of high water accumulation capacity, effective precipitation capture by slopes, and specific soil properties (volcanic soils over low-permeability glacial deposits) are critical for triggering these events. The research highlights the importance of monitoring soil moisture and surface deformation for predicting these hazards, especially under changing climate conditions.

Objective

• To investigate the interplay between geomorphological, geotechnical, and hydrometeorological factors, including precursory surface deformation, on debris flow initiation in glacio-volcanic environments of the Southern Andes, specifically focusing on the Ñisoleufu debris flow event.

Study Configuration

• Spatial Scale: Ñisoleufu zone, Southern Andes, Chile (approximately 39°S). The area affected by the debris flow was 118,575 m². Slopes varied from 0° to approximately 90°.
• Temporal Scale: The primary debris flow event occurred on 31 May 2021, with reactivations on 19 June 2023 and 28 June 2024. Sentinel-1 SAR data covered November 2020 to June 2021. Field campaigns were conducted 1 day and 3 months after the 2021 event.

Methodology and Data

• Models used:
  • Stanford Method for Persistent Scatterers (StaMPS) for InSAR processing.
  • ERA5-land product for soil moisture data.
  • SNAP packages through snap2stamps routines for SAR data processing.
  • GACOS correction (Yu et al., 2018) through the TRAIN toolbox (Bekaert et al., 2015) for atmospheric phase component reduction.
• Data sources:
  • ALOS PALSAR DEM (12.5 m resolution) for geomorphological characteristics.
  • Sentinel-2 acquisitions (13 May and 14 June 2021) for Normalized Difference Vegetation Index (NDVI).
  • Sentinel-1 C-band SAR data (35 ascending, 18 descending images from November 2020 to June 2021) for surface deformation.
  • Fieldwork: Soil sampling and laboratory analysis for geotechnical properties (density, moisture content, specific weight, granulometry, liquid limit, plastic limit, plasticity index, USCS classification).
  • Hydrometeorological data: Hourly/daily rainfall from INIA agrometeorological and DMC networks (Pucón station), Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) precipitation estimates.
  • Soil hydraulic properties measurements: Evaporation method (HYPROP®) for soil moisture and unsaturated hydraulic conductivity, KSAT® equipment (Meter Group) using the falling head method for saturated hydraulic conductivity.

Main Results

• The Ñisoleufu debris flow affected an area of 118,575 m², characterized by low positive NDVI values (< 0.20).
• Geomorphological factors, including steep slopes (up to ~90°) and northern orientation, promoted water accumulation and efficient surface drainage, leading to subsurface pore-water pressure build-up.
• Stratigraphic analysis revealed a sequence of low hydraulic conductivity glacial deposits (till, varves; 1.54 x 10⁻⁵ to 2.65 x 10⁻⁵ m s⁻¹) underlying high saturated hydraulic conductivity volcanic soils (Neltume ashfall, organic-rich; 4.64 x 10⁻⁵ to 3.31 x 10⁻⁴ m s⁻¹).
• Geotechnical analysis showed volcanic soils with moderate to high plasticity (Plasticity Index 33-36) and high liquid limits (123.93-149.83), classified as plastic silt (CH) and plastic organic soil (OH).
• ERA5-land data indicated significant short-term increases in soil moisture content at various depths (up to 2.89 m), with a 50% change shortly before the debris flow, particularly at the tephra-till/varves interface, correlating with intense rainfall.
• InSAR detected precursory surface subsidence/deformation ranging from +9 to -32 mm yr⁻¹, with a more pronounced subsidence of -85 mm yr⁻¹ in the 30 days prior to the event, consistent with soil water content changes.
• The debris flow was triggered by soil saturation, reducing effective stress and leading to extensional failure in volcanic deposits, exacerbated by the low hydraulic conductivity of underlying glacial deposits acting as a barrier.

Contributions

• Provides a comprehensive understanding of the interaction between geomorphological, hydrological, and geotechnical factors influencing debris flow behavior in glacio-volcanic environments of the Southern Andes for the first time.
• Highlights the critical role of stratified soil properties (high-permeability volcanic soils over low-permeability glacial deposits) in modulating water storage and triggering rainfall-induced debris flows.
• Demonstrates the utility of integrating multi-temporal InSAR data with hydrometeorological and geotechnical analyses to identify precursory deformation signals for debris flow initiation.
• Emphasizes the need for incorporating detailed soil and slope characteristics, seasonal soil moisture dynamics, and drought-related weakening into debris flow risk prediction models, particularly in the context of climate change.
• Offers practical criteria for hazard assessment in post-glacial volcanic terrains and contributes to the development of early warning systems for rainfall-induced debris flows in vulnerable regions.

Funding

• Agencia Nacional de Investigación y Desarrollo (ANID) of the Chilean Government
• Fondecyt Regular (grant 1230792)
• FONDEF ID23i10118
• Fondecyt post-doctoral (grant 3200387)
• CIVUR-39° “Centro Interactivo Vulcanológico de La Araucanía” Project UFRO2193 of the Desarrollo de Actividades de Interés Nacional (ADAIN), Ministry of Education, Chilean Government

Citation

@article{Fustos2025Controls,
  author = {Fustos, Ivo and Basualto, Daniel and Gatica, Ardy and Bravo-Alarcón, Alvaro and Palma, José Luis and Fuentealba, Gabriel and Sepúlveda, Sergio A.},
  title = {Controls over debris flow initiation in glacio-volcanic environments in the Southern Andes},
  journal = {Natural hazards and earth system sciences},
  year = {2025},
  doi = {10.5194/nhess-25-4843-2025},
  url = {https://doi.org/10.5194/nhess-25-4843-2025}
}

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