Effect of Melt-Domain Size on the Stability of Vapor Films: Implications for Explosive Submarine Volcanic Eruptions

Abstract

The explosivity of eruptions in the presence of external water is determined by its thermodynamic interactions with magma. Critical parameters governing an energetic magma-water interaction include the duration of water boiling regimes and the associated rate of heat transfer from magma to the water. A range of melt fragments from micron to cm-size are commonly observed during such interactions. Therefore, the melt domain- or fragment-sizes, at a given melt-water mass ratio, likely provide a first-order control on the efficiency of magma-water interactions but has remained poorly constrained. Comparing high-temperature experimental results with milimeter-scale melt domains to the existing studies with centimeter-size domains, this study provides insights into the effect of fragment size on water boiling regimes. Spherical samples of re-melted mafic rocks with an initial temperature of ~1388 K (1115 ºC) were submerged in water. The temperature of the water was varied in the range of 276-365 K (3-92 ºC) between experiments but was kept constant during any given experiment. The experimental videos were captured using high-speed cameras from where the time scales of water boiling regimes were determined. Our experimental results show that mm-scale melt fragments are associated with shorter vapor film timescales compared to cm-sizes, where this difference increases with increasing water temperature. Using the stable vapor film time scales from the experiments and heat transfer modeling, the Leidenfrost temperatures were estimated. The time scales of stable vapor films provide constraints on the time available for mixing between melt and water along with any external trigger that may be required for energetic melt-water interactions and explosive submarine volcanic eruptions.