Mapping and Predicting Debris Flows in the Central Chilean Andes

Debris flows pose major hazards in the semi-arid Andes of Central Chile. Both, their regional spatial distribution and controlling factors, however, remain poorly understood. Our contribution addresses this gap in the upper Maipo River basin – a critical basin for Santiago’s water supply and recreational activities – which has experienced recent catastrophic events in 2017, 2021, and 2023 that resulted, among others, in the complete flooding of several villages.

Using multi-temporal imagery, we mapped 312 debris flows that occurred between 2007 and 2017, and modeled their occurrence through Bayesian logistic regression. We assessed the slope, contributing area, elevation, and lithology as potential controls, while testing the efficacy of slope–area relationships for susceptible terrain identification.

Our results demonstrate that slope and contributing area are primary predictors, exhibiting a credible positive interaction. Conversely, elevation showed a negative correlation, and lithology offered only negligible predictive power. Most strikingly, slope–area plots revealed that high-probability source areas cluster within a distinct morphometric domain, thus offering a simple, yet reliable, approach for delineating hazardous terrain from topographic data.

Despite our short observational window and restriction to debris flow events below 3700 m asl, our findings may help establishing a framework for regional susceptibility assessments in high-priority basins of the Central Andes and underscore the utility of simple models and open-access imagery for hazard mapping in data-scarce mountain regions and, potentially, providing a first step towards early warning.