Unlocking magma’s secrets

Materials World magazine
,
1 Oct 2017

Peter D Lee, Yan Lavallée and Mike Burton* describe their new process for understanding how and when violent eruptions might take place.

Professors Peter Lee, Yan Lavallée and Mike Burton are using Diamond Light Source to better understand magma flows. This is leading to better eruption predictions as well as new insights and understanding of many amorphous materials from metallic to silicate glasses, and composites containing these materials. 

Volcanic eruptions are powered by magma. To predict their occurrence, the models require an understanding and quantitative description magma's flow properties of during transport and eruption. However, there are many properties of magma we still don’t fully understand. What causes it to ascend and erupt? How does magma flow? Will it erupt as a benign effusion or as a catastrophic explosive event? How long will eruptions last? All these are vital questions to more than 500 million people who live near the world’s potentially dangerous 1,500 active volcanoes, and the many more people affected by gas and ash plumes that can spread over large portions of the Earth’s atmosphere. 

The magma flows that drive these volcanic systems are complex silicate liquids that carry variable amounts of solid crystals and gas bubbles. The nature of silicate liquids has been explored extensively through the study of glass for industrial purposes. However, in natural magmas, the glasses carry crystal and bubble cargos. The interaction between all three phases is not well understood, yet has a dramatic influence on how magma behaves. For example, will it effuse as lava flow down the flank of a volcano or shatter during an explosive eruption? Generally, the more crystalline a magma, the more difficult the flow and the more likely it will break. Similarly, the bubblier a magma, the more likely it will fragment. Understanding the interactions between the liquid, crystals and bubbles is key to understanding magma behaviour, forming one of the great challenges of volcanology. 

Traditionally, volcanologists and petrologists – who study the origins of rocks – looked at volcanic rocks forensically, examining thin sections optically or with electron microscopy to correlate the mineralogy back to the eruption type. More recently, Lavallée and other volcanologists have performed experimental studies to simulate key parts of the lifecycle of magmas, from genesis, storage, evolution and transport to eruption, using sophisticated experimental apparatus in the laboratory. However, their work has been limited because they cannot observe what is happening inside the sample during a test – until now. 

Replicating the magma ascent

For almost a decade, Lee’s group has used synchrotron X-ray imaging to see inside materials as they are fabricated or during service. He specialises in making sample environments inside the beamlines at Diamond Light Source, the UK’s national synchrotron. These environments replicate processes ranging from simulating aero-engine component fabrication to
laser additive manufacturing and the conditions of magma ascent.

At the core of many of these studies is a bespoke rig called the P2R, which is designed to simulate the fabrication of superalloy components for aero-engines. It replicates a range of thermomechanical processes on the beamline while rotating with nanometre precision to allow high-speed synchrotron tomography and diffraction. Coupled with half a dozen environmental cells, the conditions from -40–1,600°C are achieved with a range of controlled atmospheres, allowing the study of ice cream processing through to nickel superalloy casting and forging. 

Funded by the National Environmental Research Council, Lee’s group worked with Lavallée and Burton to transform the P2R in-situ rig to replicate the conditions of magma ascent from a depth of 2km in the Earth, to the surface. Using Diamond, and the P2R, they can manipulate magma while ultra-fast CAT scans are taken to see inside it. This is called 4D imaging – 3D plus time – and provides them with the 3D X-ray vision needed to see into magmas as they evolve and flow.

This equipment enables volcanologists to experimentally deform magma while quantifying the interaction between liquid, crystals and bubbles in real-time. This data is being analysed with algorithms developed to quantify the growth of crystal phases in metallic alloys, providing information on the size, morphology, connectivity and growth rates. Data from metallic alloys are being used by major automotive and aerospace companies to make their components stronger and lighter, improving durability while reducing environmental impact. In volcanology, the quantification of magma evolutions provides the information needed by other groups to refine and develop new models. This is shedding new light on volcanoes, improving our ability to constrain magmatic processes, with an end goal of improving our ability to forecast volcanic eruptions. 

For example, being able to see inside magma with real-time synchrotron X-ray tomography has revealed an entirely new paradigm in the diffusion and bubble formation in these high-temperature materials. Working together, these groups are using the synchrotron to reveal groundbreaking observations on the behaviour of magma and, importantly, the vesiculation of water bubbles during shearing at magmatic conditions. Models of the Earth rely on simple petrological experiments conducted in isotopic stress fields in hydrostatic pressure vessels without shear. The new data are providing provocative evidence for the need to create new models of magma evolution during flow.

These results address a major disagreement in geosciences. Most petrologists treat magma as a material in physico-chemical equilibrium in the Earth. But volcanologists increasingly believe otherwise from their study of eruptive products. The techniques used place magma in disequilibrium by varying pressure, temperature and deformation. Synchrotron imaging has become the key to unlocking the secrets of magma evolution. 

Using Superman's X-ray vision to predict violent eruptions

The impact of the new insights into magma may be much wider than volcanology, in that the mechanisms proposed could impact any amorphous materials from metallic to silicate glasses, and composites containing these materials. The observed trends on the increased nucleation rate and growth of bubbles during continuous deformation will change our understanding of phase nucleation and diffusive transport in these materials. 

In terms of synchrotron imaging, the process replicators developed for studying magma ascent have now been used to investigate a wide range of materials, from understanding graphite growth in molten cast iron to making better bricks from foamed waste ash and glass products, to simulating the behaviour of 3D-printed titanium knee joint implants. The list continues to grow.

Indeed, using half a dozen different beamlines at Diamond, Lee and his team have now studied the processing and mechanical behaviour of light alloys for automotive applications and superalloys for aeroengines. As a result they were recognised as one of the top users in materials science during Diamond’s 10th anniversary celebrations this year. Examples include how, using the lower energy Diamond-Manchester tomography branchline, they have studied the formation of defects in the cast aluminium alloys used in suspension components in automobiles, enabling the components to be cast in high-strength alloys with excellent ductility. 

Using the in-situ heat treatments on the SAXS beamline, I22, they are now working with a major automotive company to help develop nano-precipitates that are stable at high temperatures, with a goal of developing aluminium alloys that retain their strength at 350°C to provide a significant boost to engine efficiency. In addition, using the high-energy synchrotron X-ray diffraction beamline, I15, they are working with a steel company to understand the mechanically-induced transformation behaviour of the metastable austenite phase in transformation induced plasticity assisted dual phase steels, to optimise the steel’s work hardening behaviour. 

Lee concludes, ‘Looking inside a volcano with synchrotron vision is like having Superman’s X-ray vision, lending us the “super-powers” to gain new understanding and insight into how and when violent eruptions might take place.

‘Using our process in Diamond beamlines, we are now able to see inside a range of materials in 4D, creating 3D images as the material changes over time. This allows us to change or modify materials and their behaviour as we make or use them, and improving their properties. This is just the beginning.

’*Professor Peter D Lee is the Assistant Director for Physical Sciences of the Research Complex at Harwell.

Prof Yan Lavallée is Chair of Volcanology and Magmatic Processes at the University of Liverpool.

Prof Mike Burton is Chair of Volcanology at The University of Manchester.