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Volcanoes fed by ‘mush reservoirs’ not pools of liquid magma

Volcanoes fed by ‘mush reservoirs’ not pools of liquid magma
28 Jan
Everything we thought we knew about eruptions could be wrong

There’s a rift among those in the volcanic community. While one half subscribe to the traditional assumption that within volcanoes lie chambers filled with molten magma, the other half is convinced by a more recent theory and new modelling has provided evidence for how it works.

The theory states that rather than harbouring pools of molten magma, volcanoes are actually fed by ‘mush reservoirs’ – areas of mostly solid crystals with magma in the small spaces in between. This theory is based on a number of seismic and electromagnetic tests carried out at volcanoes including Montserrat, Mount St Helens and Yellowstone, the data from which revealed a lack of ‘melt’ underground and provided no evidence for large areas of liquid.

The new mathematical models run by Imperial College London and the University of Bristol provide evidence for how mush reservoirs lead to eruptions. They demonstrate that the melted matter that does exist within a volcano percolates upwards around the solid crystals. As it does so, it transports chemical components that melt at comparatively lower temperatures to the top of the reservoir.

‘What that means is that all of the stuff that likes to melt at low temperature gets collected together at the top of the reservoir,’ explains Professor Matthew Jackson from Imperial College. ‘Some of the crystals sitting at the top of the mush reservoir are quite old,’ he adds. ‘All this melt suddenly accumulates around them that’s been percolating from deep within the mush reservoir and all they know is that suddenly they’re in magma.’ It’s this process that can eventually lead to eruption.

Jackson and his team now plan to model active volcanoes, including Santorini and Yellowstone, with the ultimate aim of predicting eruptions. ‘It would be good to know when magma is getting to the point when it’s ready to erupt again,’ says Jackson.

This was published in the February 2019 edition of Geographical magazine

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