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Effect of melt-domain size on vapor film stability with implications for explosive submarine eruptions

Rebecca Fulton , Pranabendu Moitra

Abstract

The explosivity of volcanic eruptions involving external water is primarily governed by factors like the duration of water boiling regimes and associated magma-to-water heat transfer rates. Melt fragments ranging from micron to cm-size are observed during such interactions, therefore fragment size likely provides a first order control on the efficiency of magma-water interactions. However, the impact of fragment/domain size on water boiling regimes and their timescales has remained poorly understood. This study investigates the effect of melt fragment size on water boiling dynamics using high-temperature experiments with millimeter-sized spherical, re-melted mafic rock samples (~1388 K initial sample temperature). The samples were submerged in water at temperatures ranging from ~276 to 365 K. High-speed video analysis captured the boiling regimes, allowing for the determination of vapor film timescales and comparison to existing results on centimeter-sized domains. Our experimental results reveal that mm-scale fragments cause a significantly shorter vapor film lifetime than cm-scale fragments, where this difference increases with increasing water temperature. Using the experimental data and heat transfer model, the Leidenfrost temperatures, i.e., the temperature where vapor films collapse, were estimated. Our findings provide new constraints on the time available for melt - water mixing and the potential for any necessary external triggers to initiate explosive interactions. Thus, the outcomes of this study have implications for better understanding the energetic magma-water interactions, potentially leading to explosive submarine volcanic eruptions.