Morphological and Sedimentary Responses to Lahars: Implications for Infrastructure Risk in a Changing Climate

Over 800 million people globally live within 100 km of active volcanoes. As populations grow and urban areas expand into hazard-prone regions, the risks posed by volcanic processes such as lahars are expected to increase. Lahars-rapid, gravity-driven flows of water-saturated volcanic debris-can exceed a cubic kilometre in volume and travel more than 300 km from source, dramatically reshaping landscapes, blocking river systems, and inflicting long-lasting geomorphic and infrastructural damage. While primary lahars typically follow eruptive activity, secondary lahars, which can be triggered by rainfall, glacial melt, or other non-eruptive processes, may continue to occur for decades. It is increasingly speculated that rising temperatures and shifting precipitation patterns under climate change will amplify both the frequency and magnitude of these secondary flows.

This project investigates the long-term dynamics of lahar-deposited sediment, with a primary focus on Calbuco in Chile, to understand the potential for sediment remobilisation and associated hazards under future climate scenarios. At the core of the study is the quantification of sediment volumes following lahar events. This will be achieved using remote sensing methods, particularly data from Synthetic Aperture Radar (SAR) satellites alongside high-resolution Digital Elevation Models (DEMs). A workflow for using amplitude and DEM differencing will be used to assess deposit thickness. These thickness estimates will then be translated into volumetric measurements using geometric methods, allowing for improved modelling workflow in near-real-time.

In addition to sediment volume, a central focus of the research is the persistence of this material in the landscape. By monitoring changes in SAR backscatter signals over time, we will aim to track post-lahar surface evolution, identifying signs of sediment consolidation, vegetation regrowth, or remobilisation via secondary flows and fluvial activity. These insights will be complemented by field validation in the Rio Blanco Este catchment, building on data from 2016 and conducted in collaboration with Chile's geological agency SERNAGEOMIN. The temporal evolution of sediment volume will be used to estimate sediment "half-life"-the duration over which deposited material remains unstable or available for further movement-using exponential decay models. These estimates will be refined by propagating uncertainties from both remote and field measurements, and by considering climate and terrain controls on sediment stability.

To understand how sediment remobilisation potential might change in the future, we will integrate downscaled CMIP6 climate projections for the region, focusing on precipitation trends and temperature-driven snow and ice melt-both critical triggers for lahars. These projections will inform dynamic susceptibility models calibrated with remote sensing-derived volume data and in situ observations, allowing us to estimate future lahar likelihood and potential sediment availability.
Recognising that lahars not only alter natural systems but also pose serious threats to infrastructure, the project will map critical assets such as roads, bridges, hydropower facilities, and water supply infrastructure. By overlaying hazard models onto this infrastructure inventory using GIS tools, we will identify areas of high exposure, enabling more targeted mitigation strategies and disaster preparedness.

Finally, to test the broader applicability of our methods and findings, the study will be extended to additional case study volcanoes.