Experiments on the heat discharge at the dynamic magma-water-interface

Compared to “dry” atmospheric eruption of magma or “dry” magma/rock contact, intensity and time scale of heat discharge from magma to the surroundings is strongly modified by an effective coolant: water or water‐sediment mixes. In the case of subaqueous or subglacial eruptions magma‐water contact must take place and can result in phreatomagmatic explosions. Even if no explosions occur, rapid cooling results in the formation of pyroclasts by thermal granulation. To study this process in detail, a short‐term calorimeter was built for the direct measurement of the heat‐flux from a magmatic melt to a coolant. Volcanic rocks from recent eruptions in Iceland were remelted and used to produce jets of melt poured into a coolant‐filled container. Particles could be produced in a non‐explosive process, that are practical identical to those from natural hyaloclastites. The process' fragmentation energy is about 10% of the total heat transferred from melt to coolant.