Scientists have always believed that it was water along with shallow magma stored in the Earth’s crust that pushed volcanoes to erupt.
Now, new tools have proved this theory wrong, with researchers concluding that it is carbon dioxide that triggers explosive eruptions.
A new model suggests that basaltic volcanoes are fed by a deep magma within the mantle, stored about 20 to 30 kilometres below Earth’s surface.
‘We used to think all the action happened in the crust,’ said senior author Esteban Gazel.
The new data implies that the magma comes directly from the mantle, passing fast through the crust driven by carbon dioxide gas.
‘This completely changes the paradigm of how these eruptions happen,’ said Gazel.
‘All volcanic models had been dominated by water as the main eruption driver, but water has little to do with these volcanoes. It’s carbon dioxide that brings this magma from the deep Earth.’
The findings published this week in the Proceedings of the National Academy of Sciences, could help in improving volcanic-hazard planning.
About four years ago, Gazel and Charlotte DeVitre, a postdoctoral researcher at the University of California, Berkeley, developed a high-precision carbon dioxide densimeter which measures density in a tiny vessel for Raman spectroscopy (a device that examines scattered photons through a microscope).
Natural samples from the volcanic eruption containing microscopic carbon dioxide-rich bubbles were measured using the newly developed densimeter.
For the scientists this is essentially like examining a microscopic time capsule to provide a history of the magma.
Using the new tools, the scientists studied volcanic deposits from the Fogo volcano in Cabo Verde, west of Senegal in the Atlantic Ocean.
They found a high concentration of carbon dioxide enclosed in the crystals suggesting that the magma was stored tens of kilometres below the surface within the Earth’s mantle.
This implies that eruptions such as Fogo’s volcanic flareups start and are fed from the mantle, effectively bypassing storage in the Earth’s crust and driven by deep carbon dioxide, according to the paper.
‘These magmas have extremely low viscosities and come directly from the mantle,’ said DeVitre.
Comprehending magma storage helps best prepare society for future eruptions, said Gazel.
‘Deep magma storage will not be detected by ground deformation until the melt is close to surface,’ he said.
‘This has important repercussions to our understanding of volcanic hazards. We need to understand the drivers of these eruptions. The only way to see these processes now is by observing earthquakes, but earthquakes don’t tell you exactly what’s happening.’
Gazel added that with precise measurements that tell us where eruptions start, where magmas are stored and what triggers the eruption we could develop a better plan for future eruptions.
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