Constraining the Energetics of Explosive Lava-Water Interactions

The quantitative effect of external water on volcanic systems, such as phreatomagmatic eruptions, is difficult to determine. However, explosive interactions between surface lava flows and water help inform our understanding of explosive magma-water interactions originating in the conduit or vent. In this work, we constrain the energetics of explosive lava-water interactions and compare our results with laboratory experiments that simulate melt-water explosions. We first constrain the proportion of ejecta contributing thermal energy to drive lava-water explosions (termed "active particles") and then estimate the total energy of these explosions using both laboratory-derived energy values, and theoretical thermal energy transfer estimates. We investigate energetics over a broad range, based on input parameters derived from field data. We find that the total explosion energy associated with lava-water interactions can be up to eight orders of magnitude greater than that of laboratory experiments. Although the specific thermal energy transfer (per unit mass of ejected material) of laboratory experiments falls within the range estimated for lava-water explosions, the lava-water explosions studied here occur over a range twice as large as laboratory experiments, extending the range known for natural systems. The largest specific thermal energy transfer estimate for lava-water explosions may be close to the maximum achievable in a natural system, and is almost double that of the largest estimate for laboratory experiments. Therefore, the results of lava-water explosion studies may be useful in understanding the role of external water in increasing the energetics of primary phreatomagmatic or phreatic eruptions. Additionally, with the growing concern over large lava-water explosions associated with the 2018 Leilani eruption on Kīlauea, this work can help inform safer exclusion zone distances near the shoreline, at ocean-entry sites, by providing specific energy estimates that can be applied to lava mass flux estimates at ocean entry sites.