A revisit of the role of gas entrapment on the stability conditions of explosive volcanic columns

Abstract

Highlights • We study the collapse conditions using a 1D model with grain-size distribution (GSD). • Combined effects of gas entrapment and variable entrainment favor column collapse. • This drastic effect is reduced when accounting for open porosity in the model. • We predict GSD in pyroclastic flows as a function of GSD and MDR at the vent. • We test the model against the historical 186 CE Taupo and 79 CE Vesuvius eruptions.

The Effect of Wind and Atmospheric Stability on the Morphology of Volcanic Plumes From Vulcanian Eruptions

“…All available options were used aside from particle aggregation. Although aggregation is known to be an important process in Sakurajima (Bagheri et al, ; Gilbert & Lane, ) and the total grain size distribution (TGSD) of each eruption is known to impact plume height (Macedonio et al, ; Michaud‐Dubuy et al, ), owing to the lack of concrete data and the large span of the study period, the TGSD used is the one assigned to Sakurajima by Mastin et al (), that is, 0.24, 0.25, 0.2, 0.12, 0.09, 0.0425, 0.0325, 0.0125, 0.0075, and 0.005 for ϕ ranging between −1 and 8 ( in millimeters).…”

“…In the calculations here U 0 was based on FPLUME output but the exit velocity at the vent was arbitrarily set at 120 m/s. Finally, the TGSD is known to affect plume height (Michaud‐Dubuy et al, ), but this effect was ignored due to the lack of data. For a more detailed approach on the subject, FPLUME would need to be coupled with a numerical weather prediction model to allow for high‐resolution computational experiments to mirror the controlled nature of analog experiments (e.g., Carazzo et al, ).…”

Wind Entrainment in Jets with Reversing Buoyancy: Implications for Volcanic Plumes

“…We now use the constant value of wind entrainment coefficient β found with our laboratory experiments to parameterize our 1‐D theoretical model (PPM) of explosive volcanic eruption (Michaud‐Dubuy et al, 2018), which is detailed in Appendix A. As described in Michaud‐Dubuy et al (2018), this model takes into account particle sedimentation, modulation of the effective amount of gas in the column (through gas entrapment and open porosity), as well as the variation of the entrainment coefficient α . Our theoretical analysis and laboratory experiments highlight the importance of both Ri 0 and W ∗ , a result consistent with previous studies (Degruyter & Bonadonna, 2013).…”

Impact of wind direction variability on hazard assessment in Martinique (Lesser Antilles): The example of the 13.5 ka cal BP Bellefontaine Plinian eruption of Mount Pelée volcano

“…The total grain-size distribution (TGSD) is an essential input for models of tephra transport and dispersion in the rising volcanic plume (Michaud-Dubuy et al, 2018) and the spreading umbrella cloud (Macedonio et al, 2005), as it gives the mass percentage of the different particle classes at the source. The TGSD of a given unit is calculated from the grain-size distribution of each individual sample collected in the field for this unit.…”

“…The value of the exponent D reflects the fragmentation efficiency, and thus quantifies the fraction of fine (D > 3, efficient fragmentation) or coarse (D < 3, poorly efficient fragmentation) particles in the deposit. It has been proven to control the total amount of gas available in the turbulent flow (Kaminski and Jaupart, 1998) hence to affect the maximum column height of sustained Plinian columns (Girault et al, 2014) and collapsing fountains (Michaud-Dubuy et al, 2018). This parameter is thus important to characterize the eruption dynamics.…”