Near real-time retrieval of weak plume source parameters: Insights from physical modeling and Meteosat data

The prediction of the spatial and temporal evolution of ash dispersal and concentrations during an explosive volcanic eruption is crucial for crisis management. Satellite observations of volcanic ash clouds have enabled an important advance in the near-real-time quantification of the dynamic parameters of the volcanic umbrella propagating in the atmosphere. However, the link between these observations and the estimation of the eruptive source parameters (ESPs), such as the mass eruption rate (MER), remains a scientific obstacle to be overcome.

Previous studies developed methods to estimate the MER based on the temporal evolution of the volcanic umbrella obtained by visible images. The accuracy of the predictions however strongly depends on the physical model used to link the measurements made on the umbrella to the source conditions. These methods are reliable for eruptions where the impact of wind is low on the vertical plume (i.e., producing “strong plumes”), but are less suitable for weaker eruptions and/or occurring under strong wind conditions (thus producing “weak plumes”), which are much more frequent. In this study, we use the 1-D volcanic column model PPM for the estimation of ESPs based on umbrella measurements from strong to weak plumes. PPM takes into account the precise effects of wind and particle sedimentation on the plume dynamics, and has already been validated with natural data on Plinian eruptions.

The model allows predicting the plume geometry as seen from space, but close to the eruptive vent. These predictions are then used to link the MER to the umbrella geometry far from the source via an empirical factor  that connects the conditions at the neutral buoyancy height to those at the source of the umbrella cloud. The model is calibrated and tested using Meteosat-SEVIRI (MSG) images via the HOTVOLC system of paroxysms from Mt Etna (2015-2022) and from the Soufriere Saint Vincent (2021). The model allows estimating the temporal evolution of the MER during the Soufriere Saint Vincent eruption, with values consistent with those estimated in the field. The model also provides a theoretical framework to explain the geometry of weak plumes from Mt Etna. Ultimately, this study will provide a robust tool for a rapid interpretation of satellite data in terms of source conditions, which are necessary inputs for volcanic ash transport and dispersion models, such as those used by the Volcanic Ash Advisory Centers.