Combining Spherical-Cap and Taylor Bubble Fluid Dynamics with Plume Measurements to Characterize Basaltic Degassing

Abstract

Basaltic activity is the most common class of volcanism on Earth, characterized by magmas of sufficiently low viscosities such that bubbles can move independently of the melt. Following exsolution, spherical bubbles can then expand and/or coalesce to generate larger bubbles of spherical-cap or Taylor bubble (slug) morphologies. Puffing and strombolian explosive activity are driven by the bursting of these larger bubbles at the surface. Here, we present the first combined model classification of spherical-cap and Taylor bubble driven puffing and strombolian activity modes on volcanoes. Furthermore, we incorporate the possibility that neighboring bubbles might coalesce, leading to elevated strombolian explosivity. The model categorizes the behavior in terms of the temporal separation between the arrival of successive bubbles at the surface and bubble gas volume or length, with the output presented on visually-intuitive two-dimensional plots. The categorized behavior is grouped into the following regimes: puffing from (a) cap bubbles; and (b) non-overpressurized Taylor bubbles; and (c) Taylor bubble driven strombolian explosions. Each of these regimes is further subdivided into scenarios whereby inter-bubble interaction does/does not occur. The model performance is corroborated using field data from Stromboli (Aeolian Islands, Italy), Etna (Sicily, Italy), and Yasur (Vanuatu), representing one of the very first studies, focused on combining high temporal resolution degassing data with fluid dynamics as a means of deepening our understanding of the processes which drive basaltic volcanism.