Heat source or heat sink: What dominates behavior of non-explosive magma-water interaction?

Much of the volcanism on Earth takes place in subaqueous settings where magma has direct contact with a water reservoir of restricted or quasi unrestricted volume. In order to assess the intensity and timescale of non-explosive interaction of magmatic melts and water, experiments representing these settings were performed. Natural volcanic samples were remelted and poured as a continuous jet into a water-filled calorimeter where the melt interacts with its coolant. The rapid cooling results in granulation, i.e. brittle failure of the material. Granulation needs energy, which is taken from the thermal input of the hot melt. Energy used in granulation was found to require 5%-20% of the melt's initial heat content. This energy loss fraction is insensitive to variations in coolant- and melt temperatures but instead depends on the melt's thermomechanical properties. However analysis of the experimentally produced granulate indicates a strong correlation between the initial coolant temperature -i.e. the heat sink- and the grain-size distribution, but also shows variations due to material properties. The maximum of the grain-size distribution was determined to change from a diameter of 1 mm up to 4 mm due to coolant temperature increase. Properties of the heat source (melt ) dominate the efficiency of the process, whereas both heat sink and source characteristics determine the products.