Magma-limestone interaction can trigger explosive volcanic eruptions and affect the global carbon cycle

'When we find volcanic rocks in nature with particular chemical signatures, it might signal that CO₂ was released from the upper crust. These new results are exciting because in the future they may help us to identify additional pathways in the carbon cycle', says Frances Deegan, researcher at the Department of Earth Sciences at Uppsala University.

Carbon makes its way out of Earth's interior and into the atmosphere mainly by CO₂ emissions from volcanoes. This is especially so in subduction zones, where material that was once at Earth's surface is forced downwards into Earth's interior and is partly remobilised at depth to feed volcanoes at Earth's surface. During this process, carbon is released from the down-going rocks and enters magma deep in Earth, which then rises upwards and releases its carbon load as CO₂ at subduction volcanoes.

At least this has been our general picture so far. But this is not all. Researchers from Uppsala University, the Swedish Museum of Natural History, and the National Institute for Geophysics and Volcanology in Italy have recently discovered what happens when magma is on its journey upwards through the crust and encounters rocks containing large amounts of CO₂, such as limestone or marble, which rest only a few kilometres beneath Earth's surface.

The team of scientists from Sweden and Italy replicated this process in the laboratory and found that when magma meets limestone the result is a very bubbly affair. They also discovered that when CO₂ is released from limestone at shallow levels in the crust it can trigger extreme behaviour in certain volatile elements. The extra CO₂ released during magma-limestone interaction might also be a factor in driving explosive eruptions at some volcanoes like Vesuvius or Merapi, whose roots are sitting in limestone and marble rocks. Furthermore, this extra source of CO₂ may contribute to Earth's carbon cycle, in the past and present.