Abstract
Interaction of magma with ground or surface water can lead to explosive
phreatomagmatic eruptions. Poorly understood questions of this process
center on effects of system geometry, 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 about 0.4kg
remelted volcanic rock in an open crucible, with controlled premix and a
trigger event created by a low energy air gun pellet (about 5J kinetic
energy). The new setup uses 55kg melt for interaction, and the timing
and locaiton of the magma-water premix can be controlled on a scale up
to 1m. A trigger mechanism is a falling hammer that drives a plunger
into the melt (about 28K kinetic energy). Results show intense
interaction at relatively low water to magma mass ratio. A video
analysis quantifies the rate and amount of melt ejection and compares
the 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 0.3m. A dependency of system
response on water mass flow rate was not observed.