Tephra fall probabilistic hazard maps for VEI 3 and VEI 4 eruptions at Mt. Garibaldi (Nch' k ay') volcano, British Columbia, Canada.

UNLABELLED: Following explosive volcanic eruptions, hazard from tephra fall can be widespread. Based on the geological record of past eruptions and risk to population and infrastructure, Mt. Garibaldi volcano (Nch' k ay') in British Columbia has been assigned the highest threat ranking of any Canadian volcano. However, until this contribution no hazard map exists for the volcano. In our study, we formed a government-university partnership and modelled tephra dispersion for Volcanic Explosivity Index (VEI) 3 and VEI 4 scenarios for Mt. Garibaldi to produce probabilistic tephra fall hazard maps. We found significant tephra impacts (loads ≥ 0.1 kg m- 2 which can cause skid risks on roads and disrupt airports) extend over 810 km2 for the VEI 3 scenario and 9360 km2 for VEI 4 (with 50% probability of exceedance). Tephra loads that may cause infrastructure damage (≥ 1 kg m- 2) cover 250 km2 and 1670 km2 for the VEI 3 and VEI 4 scenarios, respectively. We combined our results into a single tephra ground accumulation hazard map and information brief. This is the first probabilistic volcanic hazard map using well-constrained source parameters for a Canadian volcano. Further work with emergency managers, will build on this map, toward consideration of appropriate mitigation measures. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1186/s13617-026-00173-8.