Abstract
AbstractInteraction 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 ( ) 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.
Highlights
Explosive volcanic eruption mechanisms are difficult to address experimentally, since many of them involve processes that are important at scales of several meters to hundreds of meters
The main motivation for developing the experimental approach described here is to move towards experimental scales that can incorporate a certain amount of previously ignored complexities, such as geometrical configurations that are closer to geological situations, given uncertainties in the role of scale, geometry and timing that were described in the introduction
The luminance scale allows to quantitatively compare explosive and non-explosive system response between different experiments and different experimental setups. It is compatible with the magma-water mass ratio for the comparison of the decimeter and the meter-scale experiments
Summary
Explosive volcanic eruption mechanisms are difficult to address experimentally, since many of them involve processes that are important at scales of several meters to hundreds of meters. One such case is phreatomagmatic eruptions where magma and water interact rapidly, resulting in large scale explosions [White and Valentine, 2016]. Diatreme dimensions suggest that subsurface explosions occur at depths of km [Delpit et al, 2014; Valentine et al, 2014]. Explosions may be partially or fully contained by the host material [Graettinger et al, 2014; Sonder et al, 2015], fracturing and mixing magma and brecciated host rock [Graettinger et al, 44 2016; Sweeney and Valentine, 2015]
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