Explosive volcanic eruptions are fuelled by the escape of volcanic gases from magma stored in underground reservoirs and pipes several kilometres below the surface. Predicting such eruptions requires a real-time knowledge of just where the magma is at any one time and what it is doing.
The researchers demonstrate that as pressure decreases, crystallinity increases
Professor Jon Blundy and colleagues analysed tiny droplets of volcanic liquids that become trapped inside crystals as the magma crystallises on its way to the surface. This enabled them to reconstruct the changes in pressure, temperature and crystallinity that occur within a body of magma prior to eruption. The researchers demonstrate that as pressure decreases, crystallinity increases, and the more a magma crystallises the hotter it gets – by up to 100°C.
This surprising result indicates that the driving force behind crystallisation of these magmas was a drop in pressure, rather than a loss of heat to the surrounding rocks, as previously thought. Professor Blundy said: “This work is now being used to gauge the direction of the volcanic activity currently happening at Mount St Helens.”
This research was published in Nature 443, pp76-80.