An assessment of the effects of DEM quality and spatial resolution on a model for mapping lahar inundation areas at volcán Copahue (Argentina & Chile)

Abstract

Lahars are debris flows originating at volcanoes with very erosive and destructive capabilities. Lahars constitute a serious hazard for the communities close to the Volcán Copahue, lying at the Argentina-Chile border. This study presents a comprehensive analysis of the sensitivity of the geographic information system (GIS) assisted model LAHARZ to the spatial resolution and quality of the digital elevation models (DEMs) for mapping lahar inundation areas within the context of Volcán Copahue. In addition, critical lahar volumes required to reach the nearby settlements are investigated, following a literature review to characterize plausible triggering mechanisms. We compared lahar inundation areas at the four main catchments of Volcán Copahue resulting from five DEMs: three 30-m spatial resolution datasets (SRTM, ASTER and AW3D30), the 12-m WorldDEM™, and a 5-m DEM derived from SPOT-7 data. Our sensitivity analysis shows that DEM spatial resolution and quality precipitate into the LAHARZ results. The interaction between the spatial resolution and the channel confinement constitutes the main control of the output geometries. Higher-spatial resolution DEMs (i.e. smaller pixel size) better depict channels and better define confined channels zones resulting in narrower output areas and longer runouts. For the same volume, the inundation areas obtained using the 5- and 12-m pixel DEMs are narrower and 2–3 km longer than when derived from any of the 30-m DEMs. At unconfined channels, LAHARZ is less sensitive to the spatial resolution and inundation areas tend to show ragged edges regardless of the input DEM. The quality of the DEM controls the inundation trajectories. These results highlight the importance of evaluating topographic models for LAHARZ simulations before the implementation of the model for hazard mapping. Our results suggest that lahars of volumes of 105–106 m3 would reach the nearest villages within a radius of 15 km from the volcano. More work is required to improve the knowledge on lahar deposits and in turn hazard assessment.