An exploration of deep magmatic processes occurring in the Earth's crust beneath volcanoes, which could contribute to linking these physical processes at depth with volcanic eruptions at the surface, has been carried out by researchers from the University of Bristol and the Swiss Federal Institute in Zurich. The experimental study is published in Chemical Geology.
Volcanic eruptions represent a substantial threat for almost 500 million people living close to violently erupting volcanoes. To distinguish whether an eruption will be explosive or not, it is fundamental to explore what occurs several kilometres below the ground.
Since there is no possibility of accessing the Earth's interior directly, experiments simulating magmatic processes at depth are of vital interest. Rheology – the study of flowing material undergoing deformation – is used to constrain the physics and dynamics of magmas. The main parameter to determine in rheological investigations is viscosity, which is the internal resistance of a material to flow.
Dr Mattia Pistone of Bristol's School of Earth Sciences and colleagues show that the contemporaneous presence of crystals and bubbles induce a significant difference in the rheology of magmas with respect to two-phase (bubble or crystals + silicate melt) systems.
Crystallization and efficient gas removal from magmatic bodies lead to a substantial increase in magma viscosity and, eventually, to their 'viscous death' in the Earth's crust. On the contrary, the significant decrease of viscosity associated with the presence of limited volumes of gas could promote mobilization of the magma bodies and the generation of large explosive eruptions.
Dr Pistone said: "A possible implication of these new experimental findings is that gas-bearing magmas are rheologically mobile and may have a high tendency to feed explosive volcanic eruptions.
"For a truly multidisciplinary application to volcanic risk and mitigation, combining the experimental experience with the direct real-time monitoring of active volcanoes would greatly help volcanologists to decipher the precursor events – volcanic tremor, degassing, ground deformation – and extract from them the right information on the magmatic processes occurring at depth. This might be the first small step for multidisciplinary volcanology, but a giant leap towards volcanic forecast."
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Pistone, M et al. Rheology of volatile-bearing crystal mushes: mobilization vs. viscous death, Chemical Geology. www.sciencedirect.com/science/article/pii/S0009254113000570