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Abstract

Snow-slurry lahars, containing a mixture of water, snow, ice and debris are highly mobile for their typical volumes and occur at a rate much higher than the geologic record indicates. This hazard may cause significant proximal impacts at snow-clad volcanoes even at small volumes. However, the occurrence, footprint and intensity of snow slurry lahar hazards are generally ill-quantified due to the lack of a reliable geologic record, as most evidence disappears after melting. A potential avenue to hazard quantification is through numerical modelling. Here, we quantify snow slurry lahar hazard at Mt. Ruapehu, New Zealand through simulations to obtain lahar intensities and footprints. The most recently active vent at Ruapehu is located underneath the crater lake, which has resulted in a predisposition towards generating snow slurry lahars (e.g. in 2007, 1995, 1975, 1969). The volcano is located within a popular national park and has several ski fields on its slopes, with many assets and visitors potentially impacted by lahars. We applied a multi-phase numerical model to simulate the snow slurry lahars with a high-resolution DEM to estimate the impact of lahars on Ruapehu. Calibration and benchmarking of the model and parameters against 2007 and 1995 snow slurry lahars was used to measure simulation performance, as well as providing insights into lahar initiation and dynamics. Simulations of lahar scenarios using the calibrated parameters were then used to analyse potential impacts at Ruapehu though aggregated lahar pathways, impact footprints and measures of lahar pressure and velocity.