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 ( Lmax≥0.250.3emm2) 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.

Review of Explosive Hydrovolcanism

“…However, there may be substantial differences in the eruption physics, magma fragmentation, pyroclast transport processes and mode of deposition between eruptions in different environments [30]. The explosivity of phreatomagmatic eruptions is widely accepted to result from MFCI processes [31][32][33][34][35][36][37][38][39][40]. MFCI represents a self-driven violent interaction of magma and vaporizable water, which is sustained by thermal and hydrodynamic interaction between molten fuel (magma) and coolant (water) [41][42][43][44][45].…”

Phreatomagmatic vs magmatic eruptive styles in maar-diatremes: a case study at Twin Peaks, Hopi Buttes volcanic field, Navajo Nation, Arizona

“…The details of how this would work are unclear, but may involve sloppy strombolian bursts resulting from an entrainment of water saturated host sediments, peperite or pyroclastic deposits along with the magma, as proposed by Valentine and van Wyk de Vries (2014). Or else, ingestion of slurry or liquid water within the strombolian conduit at depth could trigger weakly explosive water-magma interactions, as experimentally obtained by Sonder et al (2018). The shift from purely phreatomagmatic activity for unit 1 to a more transitional one in unit 2 can be explained either by an increased magma flux or by a decreased water supply.…”

Vapor Bubbles and Velocity Control on the Cooling Rates of Lava and Pyroclasts During Submarine Eruptions

“…Experiments were performed with heated rock being submerged into a water channel to determine the heat transfer in nucleate boiling and nucleate flow boiling regimes. We used a low‐Si (39% SiO 2 , Sonder et al., 2018) source rock from the Knippa trap rock quarry (Balcones Igneous Province, Texas), which was readily available and was relatively homogeneous. To prepare a spherical sample (≈3 cm diameter), the rock was melted using a high temperature furnace purged with argon gas, and then poured inside a spherical mold.…”