The flow structure of jets from transient sources and implications for modeling short-duration explosive volcanic eruptions

TitleThe flow structure of jets from transient sources and implications for modeling short-duration explosive volcanic eruptions
Publication TypeJournal Article
Year of Publication2014
AuthorsChojnicki K.N, Clarke A.B, Adrian R.J, Phillips J.C
JournalGeochemistry Geophysics Geosystems
Date Published2014/12
Type of ArticleArticle
ISBN Number1525-2027
Accession NumberWOS:000348061300014
Keywordsbuoyant jets; columns; experimental volcanism; explosive volcanism; fluid-dynamics; impulsive jets; particle image velocimetry; plume; surroundings; transient volcanic plumes

We used laboratory experiments to examine the rise process in neutrally buoyant jets that resulted from an unsteady supply of momentum, a condition that defines plumes from discrete Vulcanian and Strombolian-style eruptions. We simultaneously measured the analog-jet discharge rate (the supply rate of momentum) and the analog-jet internal velocity distribution (a consequence of momentum transport and dilution). Then, we examined the changes in the analog-jet velocity distribution over time to assess the impact of the supply-rate variations on the momentum-driven rise dynamics. We found that the analog-jet velocity distribution changes significantly and quickly as the supply rate varied, such that the whole-field distribution at any instant differed considerably from the time average. We also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0.93 in an individual unsteady jet. Consequently, we conclude that supply-rate variations exert first-order control over jet dynamics, and therefore cannot be neglected in models without compromising their capability to predict large-scale eruption behavior. These findings emphasize the fundamental differences between unsteady and steady jet dynamics, and show clearly that: (i) variations in source momentum flux directly control the dynamics of the resulting flow; (ii) impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi-steady flow models. New modeling approaches capable of describing the time-dependent properties of transient volcanic eruption plumes are needed before their trajectory, dilution, and stability can be reliably computed for hazards management.

Short TitleGeochem. Geophys. Geosyst.
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