Operational Limitations of Volcanic Eruption Plume Models with a Water-Phase Transition

To apply an eruption plume model with a water-phase transition to an operational environment, we conduct an endurance test for the plume model NIKS-1D extended to include a water-phase transition (vapor, liquid, ice). The test is conducted for 28,125 synthetic eruption scenarios for 77 years of daily meteorological reanalysis for Aso volcano in Japan. Latent heat released during condensation and freezing enhances plume heights, in particular, this effect is significant for intermediate-strength eruptions (3×10⁵–10⁷ kg/s) with plumes reaching the upper troposphere. This characteristic imposes certain limitations on applying a plume model with a water-phase transition in operational environments; for plume heights of 8–15 km, corresponding to the above mass eruption rates, mass eruption rates to reproduce observed plume heights cannot always be estimated due to a discontinuity in the relationship between the mass eruption rate and plume height. Such inconsistency between the estimation and observation indicates that using a plume model with a water-phase transition in operational environments can lead to released ash profiles that deviate from reality, resulting in inaccurate ash dispersal prediction. These results highlight both the advantages and limitations of plume modeling including a water-phase transitions in operational environments.