Abstract
Determining whether magma fragments during eruption remains a seminal challenge in volcanology. There is a robust paradigm for fragmentation of high viscosity, silicic magmas, however little is known about the fragmentation behaviour of lower viscosity systems—the most abundant form of volcanism on Earth and on other planetary bodies and satellites. Here we provide a quantitative model, based on experiments, for the non-brittle, fluid dynamic induced fragmentation of low viscosity melts. We define the conditions under which extensional thinning or liquid break-up can be expected. We show that break-up, both in our experiments and natural eruptions, occurs by both viscous and capillary instabilities operating on contrasting timescales. These timescales are used to produce a universal break-up criterion valid for low viscosity melts such as basalt, kimberlite and carbonatite. Lastly, we relate these break-up instabilities to changes in eruptive behaviour, the associated natural hazard and ultimately the deposits formed.
Highlights
Determining whether magma fragments during eruption remains a seminal challenge in volcanology
Other experimental variables include the initial liquid dimensions, the extension rate and the total strain. All these variables were chosen such that our experiments cover the same range of dimensionless space and dynamical regimes as expected for natural volcanic eruptions
To determine which of these timescales controls break-up, it is useful to introduce the Ohnesorge number (Oh)—a dimensionless number that has been shown to govern the style of fluid dynamic break-up[22,32,38,39,40]: Oh
Summary
Determining whether magma fragments during eruption remains a seminal challenge in volcanology. We show that break-up, both in our experiments and natural eruptions, occurs by both viscous and capillary instabilities operating on contrasting timescales These timescales are used to produce a universal break-up criterion valid for low viscosity melts such as basalt, kimberlite and carbonatite. We relate these break-up instabilities to changes in eruptive behaviour, the associated natural hazard and the deposits formed. A robust understanding exists for the fragmentation of high viscosity, silicic systems[1,2,7,8,9,10,11]; the same theories cannot be applied to the fragmentation of lower viscosity liquids This knowledge gap is further compounded by the fact that most of the volcanism on Earth[12] and on other planetary bodies and satellites[13,14] features low-viscosity liquids.
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