Geoscientists have long thought that water – along with shallow magma stored in Earth’s crust – causes volcanoes to erupt. New research shows that gaseous carbon dioxide can trigger explosive eruptions.
The new model suggests that basaltic volcanoes, typically located on the interior of tectonic plates, are fed by a deep magma within the mantle, stored about 20 to 30 kilomteres below the Earth’s surface.
“We used to think all the action happened in the crust,” said senior author Esteban Gazel at Cornell Engineering. “Our data implies the magma comes directly from the mantle—passing fast through the crust—driven by the exsolution (the process phase of separating gas from liquid) of carbon dioxide.”
“This completely changes the paradigm of how these eruptions happen,” Gazel said. “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.”
Using new tools, the scientists studied volcanic deposits from the Fogo volcano in Cabo Verde, west of Senegal in the Atlantic Ocean. The higher amount of carbon dioxide enclosed in the observed crystals suggested that the magma was stored tens of kilometers below the surface – within the Earth’s mantle.
The team also discovered that this process is connected to the deep mantle source that supply these volcanoes.
This indicates that eruptions such as Fogo’s volcanic flare ups start and are fed from the mantle, effectively bypassing storage in the Earth’s crust and driven by deep carbon dioxide.
“These magmas have extremely low viscosities and come directly from the mantle,” said Charlotte DeVitre at University of California, Berkeley. “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. This is a major step in our understanding of the controls on basaltic explosivity.”
Comprehending magma storage helps best prepare society for future eruptions, said Gazel.
“As deep magma storage will not be detected by ground deformation until the melt is close to the 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.”
“With precise measurements that tell us where eruptions start, where magmas melt and where they are stored—and what triggers the eruption—we can develop a much better plan for future eruptions,” Gazel said.
https://phys.org/news/2023-08-carbon-dioxide-triggers-explosive-basaltic.html