Active Particle Characteristics and Energetics of Lava-Water Explosions
Abstract
Quantifying the energetics of magma-water interactions based on deposits is difficult because magmatic gas expansion and external water both contribute to the fragmentation and dispersal of tephra. However, magma-water interactions can be driven by the same mechanism as lava-water interactions and melt-water experiments, so we can use the latter to understand the former. This mechanism is Molten Fuel-Coolant Interaction (MFCI) where the "molten fuel" is magma, lava, or analog melt, and the "coolant" is external water. In this work, we investigate the characteristics of active particles, i.e., the proportion of ejecta that results from rapid thermal energy transfer that drives lava-water explosions. We then use the active particle mass and total ejecta fragmentation and dispersal to constrain the mechanical, fragmentation, and kinetic-transport energies over a broad range of explosivity. We found active particles up to 1.5 ϕ (354 μm) in size, having mossy or blocky morphologies, where blocky grains are hypocrystalline and display stepped features and/or polygonal quench cracks. These active particles make up a minimum of 1% for coarse-grained beds and up to 40% for fine-grained beds, by mass. The mass percentage of active particles displays a strong linear correlation with median grain size (r2 = 0.76). The specific mechanical energy of the lava-water explosions studied here occurs over a broader range (4 to 178 kJ/kg) than MFCI experiments, and includes updated estimates for the highest-energy lava-water explosions studied to date. Explosion energy is partitioned similarly over the two systems, with the kinetic-transport and fragmentation energy of lava-water explosions making up 25-40% and 16-55% of the mechanical energy, respectively. Studies of lava-water explosions therefore provide a field-scale analog for understanding the energetics, and therefore hazards, of MFCI in natural systems.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMV008.0009F
- Keywords:
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- 8404 Volcanoclastic deposits;
- VOLCANOLOGY;
- 8428 Explosive volcanism;
- VOLCANOLOGY;
- 8445 Experimental volcanism;
- VOLCANOLOGY;
- 8486 Field relationships;
- VOLCANOLOGY