CO2 triggers explosive volcanoes — this changes what we knew

In a new study, geoscientists disrupt long-standing notions surrounding volcanic eruptions. 
Sade Agard
Explosive lava spews from the latest eruption of the Fogo volcano located on the Cape Verde islands in November 2014. Science now knows that carbon dioxide – instead of water – triggered it.
Explosive lava spews from the latest eruption of the Fogo volcano located on the Cape Verde islands in November 2014. Science now knows that carbon dioxide – instead of water – triggered it.

Ricardo Ramalho/Cardiff University 

In a recent study published in the National Academy of Sciences, geoscientists have disrupted long-standing notions surrounding volcanic eruptions. 

For decades, water and shallow magma within the Earth's crust were believed as the main instigators of volcanic activity. However, these findings introduce a novel contender: gaseous carbon dioxide. 

The study provides a clearer understanding of Earth's inner workings, which has implications for devising improved strategies for volcanic hazard preparedness.

Meet the CO2 'densimeter'

The new model proposes that basaltic volcanoes, commonly located within tectonic plates, are fueled by deep-seated magma residing approximately 20 to 30 kilometers beneath the Earth's surface. 

"This completely changes the paradigm of how these eruptions happen," said senior author Esteban Gazel, at Cornell University, in a press release

"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."

Gazel, alongside Charlotte DeVitre, a postdoctoral researcher at the University of California, Berkeley, pioneered an advanced carbon dioxide densimeter. 

This innovative device gauges density within a minuscule container, specifically designed for Raman spectroscopy which studies scattered photons through a microscope. 

Essentially, they could peer into microscopic carbon dioxide-rich bubbles preserved in volcanic crystals, offering insights into magma history.

Additionally, the researchers devised techniques to study laser heating's impact on carbon dioxide-rich inclusions found enveloped in crystals. 

They accurately assessed melt inclusion and bubble volumes, even creating an experimental reheating method to enhance precision and account for carbon dioxide trapped as carbonate crystals within the bubbles.

Cabo Verde's Fogo volcano

With these innovative tools, they examined volcanic remnants from Cabo Verde's Fogo volcano, situated west of Senegal in the Atlantic Ocean. These investigations revealed substantial concentrations of volatiles within minute melt inclusions.

CO2 triggers explosive volcanoes — this changes what we knew
Cape Verde, isle of Fogo, Senegal

Crucially, the heightened presence of carbon dioxide trapped in the crystals hinted at magma storage deep within Earth's mantle, tens of kilometers below the surface.

"These magmas have extremely low viscosities and come directly from the mantle," DeVitre explained. "So here, viscosity and water cannot play the common roles that they do in shallower and/or more silicic (rich in silica) volcanic systems. 

"Rather, at Fogo volcano, the magma must be driven up fast by the carbon dioxide, and this likely plays a significant role in its explosive behavior."

To conclude, Gazal emphasized that with precise measurements that tell us where eruptions start, where magmas melt, and where they are stored – and what triggers the eruption – scientists can significantly improve mitigation strategies for future volcanic eruptions.

The complete study was published on August 7 and can be found here.

Study abstract:

Constraining the volatile content of magmas is critical to our understanding of eruptive processes and their deep Earth cycling essential to planetary habitability [R. Dasgupta, M. M. Hirschmann, Earth Planet. Sci. Lett. 298, 1 (2010)]. Yet, much of the work thus far on magmatic volatiles has been dedicated to understanding their cycling through subduction zones. Further, studies of intraplate mafic volcanism have disproportionately focused on Hawaii [P. E. Wieser et al., Geochem. Geophys. Geosyst. 22, e2020GC009364 (2021)], making assessments of the overall role of intraplate volcanoes in the global volatile cycles a challenge. Additionally, while mafic volcanoes are the most common landform on Earth and the Solar System [C. A. Wood, J. Volcanol. Geotherm. Res. 7, 387–413 (1980)], they tend to be overlooked in favor of silicic volcanoes when it comes to their potential for explosivity. Here, we report primitive (olivine-hosted, with host Magnesium number – Mg# 78 to 88%) melt inclusion (MI) data from Fogo volcano, Cabo Verde, that suggest that oceanic intraplate silica-undersaturated explosive eruptions sample volatile-rich sources. Primitive MI (melt Mg# 70 to 71%) data suggest that these melts are oxidized (NiNiO to NiNiO+1) and very high in volatiles (up to 2 wt% CO2, 2.8 wt% H2O, 6,000 ppm S, 1,900 ppm F, and 1,100 ppm Cl) making Fogo a global endmember. Storage depths calculated from these high volatile contents also imply that magma storage at Fogo occurs at mantle depths (~20 to 30 km) and that these eruptions are fed from the mantle. Our results suggest that oceanic intraplate mafic eruptions are sustained from the mantle by high volatile concentrations inherited from their source and that deep CO2 exsolution (here up to ~800 MPa) drives their ascent and explosivity.

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