Crystals formed in magma deep within volcanoes promise to help scientists better predict when volcanic eruptions will occur, researchers have discovered. More than 500m people live close to volcanoes that may erupt with little or no clear warning. Active volcanoes are monitored by a variety of techniques such as seismicity – the study of earthquake activity – ground tremors and gas flux, where any change from background must be large enough to be detected at the Earth’s surface.
However, ‘crystal forensics and diffusion chronology allow us to interrogate the erupted products, which represent the quench magma and provide an independent line of evidence,’ explains Kate Saunders, one of the study authors at the department of earth sciences at the UK’s University of Bristol.
Saunders and colleagues chemically fingerprinted iron–magnesium silicate crystals from previous eruptions at Mount St Helens, an active volcano in the Pacific Northwest of the US and discovered that peaks in crystal growth corresponded to increased earthquake activity and SO2 levels (Science, doi:10.1126/science.1220066). Zoned crystals grow in stages, similar to tree rings, with each zone reflecting the physical conditions within the magma chamber, Saunders explains. ‘However, we can’t just count the number of zones; we have to model the chemical exchange of elements between two adjacent zones, which is a time-dependent process.’
As well as modelling this diffusion process, the group analysed the crystals by a combination of scanning electron microscopy (SEM) and electron probe micro-analyser (EPMA) techniques. ‘Diffusion chronometry is a rapidly expanding field,’ Saunders says. ‘If the analytical facilities are available to the volcano observatories, they could start using the technique tomorrow if they wish.’