Short Time Physics During Fragmentation of Basaltic and Intermediate Magma

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The transition from continuous deformation to brittle failure of magma is common to all types of explosive volcanic eruptions. But what determines how stress is distributed in the magma volume? How much energy is necessary for continuous deformation and for fragmentation? To address such questions an experimental apparatus was built at the Universität Würzburg driving a melt plug at eruption temperatures from rest through the continuous deformation regime into brittle failure. This process was recorded by high-speed pressure- and force sensors, and a high-speed video system. It was possible to measure the critical deformation rate as well as the specific fragmentation energy, and to apply this energy to natural volcanic settings in order to assess the overall energies involved in explosive volcanic eruptions. Further questions arise from these experiments: What is the influence of magma elasticity, -viscosity, geometrical confinement and vesicularity/porosity? Therefore the above described experiment must be extended in several points. It is intended to be called STAHL ("Short Timescale Accelerated High Load") experiment, and will be tested against selected natural volcanic materials with well known properties, as well as materials of current interest (e.g. from the well documented Eyjafjallajökull 2010 eruptions). Finally the results can be scaled to natural volcanic scenarios and serve as input parameters for large scale experiments and numerical simulations. We hope to find answers to questions like: "How much energy needs to be payed to produce volcanic ash?"