Experimental delineation of gas-particle coupling regimes in explosive volcanic eruptions

Alatorre-Ibarguengoitia, Miguel A.; De Arcia, Paulina; Dingwell, Donald B. und Ramos-Hernandez, Silvia G. (2022): Experimental delineation of gas-particle coupling regimes in explosive volcanic eruptions. In: Journal of Volcanology and Geothermal Research, Bd. 431, 107654

Abstract

The kinematic and thermal coupling between pyroclasts and gas is one of the main controlling factors in the dynamics of explosive volcanic eruptions. Here, we performed rapid decompression experiments in a shock-tube apparatus at eruptive pressures (2-11 MPa) using monodisperse volcanic particles (grain-size 0.063-1.4 mm). We systematically investigated the coupling of these particles with the gas phase by measuring the rarefaction speed and the ejection velocity of the particles front in each experiment. The results are consistent with a theoretical model derived from the pseudogas approximation (i.e. perfect coupling) only for particles smaller than a certain size: similar to 0.125 mm for rarefaction speed and similar to 0.5 mm for the particles front ejection velocity, whereas larger particles are significantly decoupled. We present an experimental parameterization to calculate the kinematic Stokes number (St(k)). We show that: 1) for the ejection process the particles are coupled with the gas if St(k) < 1, whereas for the rarefaction speed the particles are fully coupled when St(k) < 0.2;2) for the rarefaction speed there is a transition when 0.2 < St(k) < 1;and 3) in both processes particles are decoupled when St(k) > 1. Furthermore, where the Reynolds number based on the relative velocity between gas and particles (Re-p) is larger than 10(3), the ratio between the timescales required for thermal and kinematic equilibration increases with Re-p, such that some particles are coupled with the gas but decoupled from it thermally. These findings represent the first experimental delineation of kinematic and thermal coupling regimes between volcanic particles and gas and contribute thereby to a more robust basis for multiphase explosive eruptive models.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 0377-0273
• Sprache: Englisch