Meter-Scale Experiments on Magma-Water Interaction

Abstract

Interaction of magma with groundwater or surface water can lead to explosive phreatomagmatic eruptions. Questions of this process center on effects of system geometry and length and time scales, and these necessitate experiments at larger scale than previously conducted in order to investigate the thermohydraulic escalation behavior of rapid heat transfer. Previous experimental work either realized melt-water interaction at similar meter scales, using a thermite-based magma analog in a confining vessel, or on smaller scale using ≃0.4 kg remelted volcanic rock in an open crucible, with controlled premix and a ≃5 J kinetic energy trigger event. The new setup uses 55 kg melt for interaction, and the timing and location of the magma-water premix can be controlled on a scale up to 1 m. A trigger mechanism is a falling hammer that drives a plunger into the melt (≃28 J kinetic energy). Results show intense interaction (L max ≥ 0.25 m 2 ) at relatively low magma/water mass ratio. A video analysis quantifies rate and amount of melt ejection and compares results with those using the same melt in the smaller scale setup. Experiments show that on the meter scale intense interaction can start spontaneously without an external trigger if the melt column above the initial mixing location is larger than 0.3 m. Experiments suggest that buoyant rise of water domains in a melt column could promote explosive interaction. We assess interaction scenarios between introduced water domains and a magma column, some of which could result in eruptions of Strombolian style, promoting brecciation and incorporation of wall rock debris into a magma column.

Fragmentation versus Cohesion

“…The key quantity is the surface density of the holes, or inter-hole centre distance λ. It is easy to see that, by volume conservation, the average diameter d of the ligaments formed from a sheet with thickness h is (Gonnermann 2005) and re-created artificially (Sonder et al 2018). (iv) Explosion of a cohesive ball of metal spheres (Frost et al 2007).…”

“…This configuration is the three-dimensional analogue with liquids of the ring configuration initially imagined by Mott (1947) for solids in two dimensions (see also Grady (2006) and Zhang & Ravi-Chandar (2007, and § 2.3 for its discrete version with magnets). This problem, in which the envelope fragment distribution is the result of a competition between deformation and cohesion, is relevant to a collection of phenomena spanning over a broad range of length scales, among which are: exploding blood cells and bacteria (antibiotics like penicillin disrupt cell walls by explosive lysis, Flores-Kim et al (2019)), spore dispersal from plants (Ingold 1971;Hassett et al 2013), boiling droplets (Frost 1988;van Limbeek et al 2013;Antonov, Piskunov & Strizhak 2019), underwater explosions (Cole 1948), magma eruption in volcanoes (Kedrinskii 2009;Sonder et al 2018), up to the torn patterns of supernovae in the Universe (Burrows 2000), among other examples. Case shells, bombs are obvious examples where one would like an a priori knowledge of the final fragments as a function of the energy released by the explosion, and of the physical properties of the enclosing envelope (Zeldovich & Raizer 2002;Kedrinskii 2005;Frost et al 2007).…”

Study on large‐scale steam explosion of molten aluminum and water

“…It was well known that there is a scale effect in melt‐water explosions 20 . In this section, the carbon steel vessels were used, and the melt was kept to 750 ~ 800°C, close to that of the casting process.…”