Explosive thermal interactions between molten lava and water

The most effective volcanic eruptions are the phreatomagmatic explosions. In such eruptions, magma and groundwater come into contact with each other, leading to explosions. A reproduction of such explosive interactions between lava (produced by remelting of volcanic rocks) and water in the laboratory was carried out, in which water was injected into molten lava. The amount of lava that was involved in the interactions, the so-called interactive lava mass, was determined. The influences of chemical composition and temperature of the melt and the injection velocity of water were also investigated.

Experiments show that an enhancement of the injection velocity of the water leads to more violent explosions. This is obviously due to an enlargement of the mixing region between water and molten lava in the crucible. Raising the temperature of the lava melt leads also to a greater impulse but not to an increase in the interactive masses as is found in connection with the water injection velocity. That means that the conversion ratio will be larger for higher lava temperatures than for lower ones.

By a fitting calculation with the measured curve of the force history of an explosive thermal interaction, the mass of water that was evaporated by the thermal interaction was estimated. In the same calculation the superheating temperature of this evaporated water can be determined. Furthermore, the amount of energy released by the explosive thermal interactions was calculated by using the measured impulse and determined fragment mass in fragmentation analysis.