Premixing of magma and water in MFCI experiments

Abstract

 Experimental studies have been performed to evaluate pre-explosive water–melt mixes with respect to explosive volcanic molten–fuel–coolant interaction (MFCI), i.e., phreatomagmatic explosion. Remolten ultrabasic volcanic rock was used as a magma simulant. Measurement of the explosion intensity was used to determine optimal premixing conditions. A well-defined optimal range was found for the hydrodynamic mixing energy (differential flow speed of 4.2 m/s), as well as for the water/melt mass ratio (0.03 to 0.04) under experimental conditions. The mass flux of water had a minor influence on the explosion intensity. Additionally, transparent mixing experiments with silicon oil and inked water were carried out. They indicate a direct dependence of the pre-explosive water-melt interface area on the explosion intensity. The experimental results show that the contact conditions of water and melt required for explosive MFCI may easily be established in natural volcanic systems. Thus, explosive MFCI is a probable mechanism of explosive volcanism.