Unravelling magmatic processes

Studies into lava flow are fundamental to understanding the processes that shape our dynamic Earth. In particular, knowledge regarding the stresses under which magma behaves in a ductile or brittle manner is of paramount importance for volcanology, geodynamics and planetary sciences. Strong focus is placed on investigating the range of the brittle–ductile transition zone.

Against this backdrop, scientists initiated the EU-funded project 'Rheophysics and energy of magmas' (RHEA). They sought to separate the stable from metastable flow field of crystal-bearing melts and estimate the onset of brittle behaviour. To help with this, work was geared towards investigating experimentally and numerically the energy distribution within magmas.

Scientists compared numerical simulations to samples deformed 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 magmatic chamber to emplacement.

The project team performed the first consistent study linking magma brittle onset to crystal fraction. 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 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 scientists investigate the suspension viscoelastic properties for various crystal fractions and determine the onset of non-Newtonian behaviour for particle-bearing fluids.

RHEA greatly contributed to enhancing understanding of the processes involved during magma deformation. The developed models should find application in a broad range of Earth science fields.