Compared the eruptive column models developed by the international volcanological community to improve the estimates of the risk for aviation and the dangers associated with the fallout of lapilli and ash. The results of the study, coordinated by INGV and the University of Tokyo, have been published in a special volume of the Journal of Volcanology and Geothermal Research
Although the first description of an eruptive column dates back to Pliny the Younger in his letter to Tacitus where he described the eruption of Vesuvius in 79 AD, the accurate understanding of the dynamics of eruptive columns, produced during explosive volcanic eruptions, still represents one of the most important challenges of modern volcanology, also for the implications it has on the risk for aviation, linked to ash emissions and, in general, on the dangers associated with the fallout of lapilli and ash.
To make a comparison of the eruptive column models developed by international volcanological communities, a study coordinated by the National Institute of Geophysics and Volcanology (INGV) - Bologna section and by the University of Tokyo. The results of this comparative work, promoted by the Tephra Hazard Modeling Commission of the International Association of Volcanology and Chemistry of Earth Interior (IAVCEI), have been published in special volume 326 of the Journal of Volcanology and Geothermal Research (http://www.sciencedirect.com/science/journal/03770273/326). The volume, which presents the results of this international collaboration lasting over two years, contains 12 scientific articles, 8 of which with the participation of INGV researchers.
“The dynamics of the eruptive columns”, explains Antonio Costa, INGV researcher and coordinator of the study, “are significantly influenced by the complex interactions between them and the surrounding atmosphere. Understanding these dynamics is essential for estimating the mass flow of fragmented material (tephra) released during eruptions, a crucial quantity for tephra dispersion models used for aviation risk estimation and hazards associated with fallout. lapilli and ashes”.
For these reasons, several eruptive column models have been developed in recent decades ranging from simple empirical models to the most recent models based on computational fluid dynamics.
“The study compares the results of the empirical parameterizations (0D models), used to estimate the mass flow of the column from the estimation of its height, with those of the simulations of one-dimensional (1D) and three-dimensional (3D) numerical models under different volcanological conditions and meteorological events, with the aim of evaluating the robustness of the models and the aspects that require improvement and future research. In particular, the study involved four 0D models, nine 1D models and four 3D models,” continues Costa.
“One of the unexpected results of the study is that “weak” (i.e. characterized by low mass flows) and “strong” (characterized by high mass flows) eruptive columns, regardless of wind conditions, are governed by processes of engulfment of the very different air, which are not always well captured by the parameterizations currently in use, thus highlighting the need for further research in this field”, continues the researcher.
Furthermore, the comparison with the 3D models clearly showed the inadequacy of the current simplifications used by the 1D models in describing the dynamics of columns with higher mass flows.
“These results have strong practical implications as several models compared in the study are commonly used to estimate mass fluxes during explosive eruptions and the estimation of these fluxes is crucial information for ash dispersion models used for transport predictions. of volcanic clouds to mitigate the risk associated with the effect of ash on planes”, concludes Costa.
Abstract
This study compares and evaluates one-dimensional (1D) and three-dimensional (3D) numerical models of volcanic eruption columns in a set of different inter-comparison exercises. The exercises were designed as a blind test in which a set of common input parameters was given for two reference eruptions, representing a strong and a weak eruption column under different meteorological conditions. Comparing the results of the different models allows us to evaluate their capabilities and target areas for future improvement. Despite their different formulations, the 1D and 3D models provide reasonably consistent predictions of some of the key global descriptors of the volcanic plumes. Variability in plume height, estimated from the standard deviation of model predictions, is within ~20% for the weak plume and ~10% for the strong plume. Predictions of neutral buoyancy level are also in reasonably good agreement among the different models, with a standard deviation ranging from 9 to 19% (the latter for the weak plume in a windy atmosphere). Overall, these discrepancies are in the range of observational uncertainty of column height. However, there are important differences amongst models in terms of local properties along the plume axis, particularly for the strong plume. Our analysis suggests that the simplified treatment of entrainment in 1D models is adequate to resolve the general behavior of the weak plume. However, it is inadequate to capture complex features of the strong plume, such as large vortices, partial column collapse, or gravitational fountaining that strongly enhance entrainment in the lower atmosphere. We conclude that there is a need to more accurately quantify entrainment rates, improve the representation of plume radius, and incorporate the effects of column instability in future versions of 1D volcanic plume models.
Fig. 1 from De Michieli Vitturi et al. (2016) JVGR, p. 77-91, Vol. 326:
A. Aerial view showing Shinmoe-dake volcano peak erupting between Miyazaki and Kagoshima prefectures on January 27, 2011 (REUTERS/Kyodo)
B. The June 12, 1991 eruption column from Mount Pinatubo taken from the east side of Clark Air Base. US Geological Survey Photograph taken by Richard P. Hoblitt
Fig. 2 Cover of special volume 326 of the Journal of Volcanology and Geothermal Research