Experimental studies of heat transfer at the dynamic magma ice/water interface: Application to subglacially emplaced lava

Experiments simulating processes operating in volcano-ice interactions were carried out to explain and quantify lava thermal properties and processes of heat transfer from pure lava melt to water and ice and from hot crystalline lava to water. The samples used (70-200 g) were obtained from an intermediate lava flow (benmoreite-trachyte) that was emplaced under and within the outlet glacier Gígjökull in the 2010 eruption of Eyjafjallajökull. Experiments involved settings with direct contact between ice and lava, and settings where melt and ice were separated by a few centimeters. Direct contact involved melt being emplaced on ice and ice placed on melt. The direct contact experiments provided initial heat flux of up to 900 kW m^-2 at an initially lava melt surface temperature of 1100°C, declining to <100 kW m^-2 at 200-300°C within 1-2 min, while the experiments without melt-ice contact yielded an initial maximum of 100-180 kW m^-2 dropping to 50-80 kW m^-2 in 2-3 min. In other experiments, where cubes of hot crystalline lava were subjected to forced convection of water at initial temperature of 20-30°C, initial heat fluxes of 400-770 kW m^-2 were followed by fast decline to <100 kW m^-2 in 15-35 s, the rate depending on cube size. The hot rock experiments provided thermal conductivity values of 1.2-1.7 W m^-1K^-1 and diffusivity of about 9 × 10^-7 m²s^-1. Values for heat flux obtained in these experiments are in the same range as those obtained from field observations of the lava emplacement in the Eyjafjallajökull 2010 eruption.