Unravelling magmatic processes
Studies into lava flow are fundamental to understanding the processes that shape our dynamic Earth. In particular, determining the stresses under which magma behaves in a ductile or brittle manner and the range of conditions appropriate to the brittle–ductile transition is of paramount importance for volcanology, geodynamics and planetary sciences. Against this backdrop, the EU-funded project 'Rheophysics and energy of magmas' (RHEA) was initiated to separate the stable from the metastable flow field of crystal-bearing melts and to estimate the onset of brittle behaviour. To establish this, work was geared towards investigating experimentally and numerically the energy distribution within magmas. Numerical simulations were compared to samples deformed experimentally at high pressures and temperatures, thus gaining better insight into the processes involved during magma deformation. In particular, RHEA developed one of the first numerical rheometers for measuring magmatic suspensions based on real measurements and formulated new laws for larger-scale models. Project members employed a finite element method to model suspension micro-hydrodynamic behaviour. Another technique based on smoothed-particle hydrodynamics was used to compute flows. Although this method focused on gravity mass flow deposits, the developed code can potentially investigate the flow dynamics from the magma chamber to emplacement. The project team performed the first consistent study linking the onset of brittle behaviour to the crystal fraction in the magma. Experimental testing included production of well-controlled synthetic magmas with various crystal fractions. A high-temperature, high-pressure Paterson press allowed measurement of viscosity. Additional strength tests using a cone-and-plate experimental apparatus were performed using various analogue fluids. Particles such as hollow spheres, glass beads and plastic particles helped mimic the whole range of magma behaviour. Oscillatory measurements helped to investigate the viscoelastic properties of the suspension for various crystal fractions and to determine the onset of non-Newtonian behaviour for particle-bearing fluids. RHEA greatly contributed to enhancing the understanding of processes involved during magma deformation. The developed models should find application in a broad range of Earth science fields.
Keywords
Magmatic processes, volcanic eruptions, lava flow, magma, brittle–ductile transition, rheophysics, energy of magmas, magma deformation, crystal fraction, Earth science
