Mobilising magma in the largest eruptions: Quantifying critical processes using in situ real time x-ray tomography

Volcanic eruptions are one the most powerful and impressive natural phenomena, and even relatively small eruptions can have major global impacts. The magma stored beneath volcanoes is an evolving mixture of molten rock (liquid), crystals (solid) and bubbles (gas). As magma cools the number of crystals increases and in principle, when magma reaches ~45% crystals the crystals jam together, 'locking up' and making it too stiff to move: the magma becomes 'uneruptible'. However, some of the most devastating explosive eruptions (including the largest super-eruption ever known) erupt large volumes (100-5000 km3) of this 'uneruptible' crystal-rich (45-60%) magma. So how do these crystal-rich eruptions happen? What lets the magma move?

As we cannot visit a magma chamber, laboratory experiments with natural rock samples and synthetic approximations (analogues) are used to simulate what is happening beneath the volcano. From these experiments, we have developed models that describe how crystal-poor magma will flow when a force is applied (its rheology). However, these rheological models fail for more crystal-rich magma (concentrated suspensions). It is thought that in crystal-rich systems the magmas ability to move is critically controlled by the crystal-crystal, crystal-bubble and bubble-bubble interactions, and the variable spatial distribution of the crystals, bubbles and melt within the sample. In one hypothesis a build-up of pressure drives bubbles through the crystal network, and causes the network to break into pieces. Despite still having the same high crystal content, deformation can then occur in the crystal-poor regions between the pieces, and the magma becomes mobile.

Crystal-rich magmas and their analogues are opaque, and conventional experimental methods do not allow us to observe the internal micro-scale processes. Therefore we have only been able to quantify the average behaviour of a volume of magma. While many possible microstructural interaction processes have been hypothesised, they remain untested. In this project the equipment used for conventional rheological experiments will be modified to allow the collection of 3D images in real time using X-ray computed Micro-Tomography (XMT). At the Diamond Light Source synchrotron facility this revolutionising imaging technology can capture the 3D internal structure of a sample (i.e. the distribution of crystals, bubbles and melt in a magma) in as little as a few seconds: producing a 3D 'movie' of what happens when the magma is deformed. By applying standard image analysis techniques to the 3D images captured over the course of an experiment, the distribution of bubbles, crystals, and melt can be quantified; every crystal and bubble can be tracked through time; and the nature of every interaction can be identified. For the first time we will be able to see what is happening inside the magma in 4D (3D + time).

By working with analogue materials, and systematically testing the microstructural behaviour as we change the crystal content, crystal shape, bubble volume and a range of other parameters known to vary in magma chambers (e.g. temperature, pressure) the high speed 4D data will be used to map out the nature and importance of the different interactions, and define the role of micro-scale variability (phase distributions and interactions) on flow. These data will be used to build a new generation of rheological models that describe the mobility of complex two- and three-phase concentrated magmatic suspensions based on an accurate understanding of the microstructural physics and micro-scale variability. By running 4D experiments on natural samples and testing the model against the results, the project will identify the conditions under which crystal-rich magmas can erupt, and begin to identify the magmatic processes that lead to the most devastating eruptions.

This project will deliver methodologies, equipment and techniques with cross-disciplinary impact, and marks a world-wide academic advancement - in line with RCUKs impact objective. The volcanology impacts will help develop more robust forecasting models with associated economic and societal impact. Beyond volcanology, it will produce a new generation of models that describe the behaviour of concentrated two- and three-phase suspensions that will be applicable to other fields (civil engineering, materials science, food science). It enables in situ observation during rheometric tests and provides an image analysis 'toolbox' for analysing these data. Specific societal and economic impacts include:

1) Industries using complex multi-phase fluids/suspensions (concrete, foodstuffs, ceramics casting etc.) will gain new models of rheological behaviours that are applicable to other systems. They also gain a technical capability to perform in situ rheometry experiments for understanding other complex multiphase fluids (XRheo). Better understanding of rheological behaviour allows proceses optimisation, targeted design, and efficiency/energy savings.

2) The XRheo has the potential to become a widely used technology for industrial and academic applications. Leading UK based equipment manufacturers [Severn (furnace design), Brookfield & Malvern (rheometric testing), Deben & Instron (precision in situ testing)] could commericalse this technology; enhancing their economic competitiveness. Alternatively, Durham University could develop a spin out company for commercialisation.

3) The scientific outputs from the project will ultimately contribute to improving volcanic forecasting and hazard assessment models. This will support policy-makers, government agencies, NGO's and disaster relief charities, the insurance, aviation & transport industries, and will deliver more effective of public services and policy implementation both nationally and internationally. Volcanic forecasting is a highly visible element in managing the commercial transport networks (passenger and freight airlines) needed to maintain UK and international economic performance. Ultimately impact in this sector will mean improved risk mitigation, and reduced danger to life. The applicant already has links to several volcanic risk stakeholder-focussed consortia (STREVA, FutureVolc, Vuelco), and associated agencies (INGV, Icelandic Meteorological Office, BGS, USGS) which will be maintained.

4) The UK suffers from a lack of numerate graduates for the wider workforce. This project will deliver wider UK socio-economic by maintaining the international profile of UK research PLC, thereby attracting the best UK and international staff and students. It provides training on world class facilities to undergraduate and postgraduate students, delivering technical and analytical skills that will make them highly employable in any sector. The Fellow will also gain managerial, networking and communication skills to support her future career, and the future generations of students that she will help train.

5) Volcanic awareness within the general public has increased significantly in recent years, and access to cutting edge research through the highly interactive outreach activity will help increases scientific engagement, encourage analytical thinking and inspire the next generation of researchers.