PREMIXING OF MAGMA AND WATER IN MFCI EXPERIMENTS

Experimental studies have been performed to evaluate pre-explosive wat er-melt mixes with respect to explosive volcanic molten-fuel-coolant i nteraction (MFCI), i.e., phreatomagmatic explosion. Re-molten ultrabas ic volcanic rock was used as a magma simulant. Measurement of the expl osion intensity was used to determine optimal premixing conditions. A well-defined optimal range was found for the hydrodynamic mixing energ y (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. Additional ly, transparent mixing experiments with silicon oil and inked water we re carried out. They indicate a direct dependence of the pre-explosive water-melt interface area on the explosion intensity. The experimenta l results show that the contact conditions of water and melt required for explosive MFCI may easily be established in natural volcanic syste ms. Thus, explosive MFCI is a probable mechanism of explosive volcanis m.