Volcanoes that sit within the Earth’s tectonic plates do not erupt as scientists thought they did. It turns out that magma in these volcanoes is driven up and out of the ground by carbon dioxide — not by water, as previously thought, a new study shows.
This magma also shoots up from much deeper reserves than previously estimated, originating in the Earth’s mantle at depths of 12 to 19 miles (20 to 30 kilometers), rather than in the outer crust, 4 to 8 miles (7 to 13 km) depth.
“This completely changes the paradigm of how these outbreaks happen,” the study’s co-author Esteban Gazellea professor of engineering in the Department of Earth and Atmospheric Sciences at Cornell University, said in a statement. “All volcano models have been dominated by water as the main driver of the eruption, but water has little to do with these volcanoes. It is carbon dioxide that brings this magma from the deep earth.”
Researchers had have already suggested that CO2 could fuel this type of eruptiontipped off by the discovery that extremely explosive eruptions do not always have the highest concentrations of water in the lava, but the new study finally confirms this theory.
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The discovery relates to basaltic volcanoes sitting within tectonic plates rather than on their edges. Basaltic volcanoes spew lava that has a lower viscosity than other volcanoes, meaning it is runnier and travels faster. These volcanoes can be very explosive when they erupt, especially if the lava is relatively cool and rapidly rises to the surface, leading to the formation of crystals that are then thrown across the landscape.
Despite making up more than half of the world’s volcanoes, basaltic volcanoes are little studied compared to those that produce viscous lava, according to the new study.
Better planning for future outbreaks
Examples of basaltic volcanoes include Kilauea and Mauna Loa volcanoes in Hawaii, as well as Pico do Fogo — a volcano on the island of Fogo in the Cabo Verde archipelago in the Atlantic Ocean — that researchers examined in a study published Monday (Aug. 7) in the journal PNAS.
Pico do Fogo is one of the world’s most active sea island volcanoes, with 30 known eruptions since records began in the 15th century, according to the study. The final eruption ended in 2015 after coating flowing lava over more than 1.5 square kilometers (4 square kilometers) of land and two villages.
The researchers analyzed the composition of small pockets of molten lava trapped in rocks on Fogo and found that they contained large amounts of CO2 that had crystallized at a pressure consistent with a depth of 12 to 19 miles. This suggested that magma had risen from within the mantle rather than from the crust. While scientists believed that the separation of water into gas and liquid drove magma up through the ground, this process, known as exsolution, occurs in the Earth’s crust. Taken together, these results indicated that CO2 bubbles propel magma from deep within the mantle.
“We used to think that everything happened in the Earth’s crust,” Gazel said. “Our data suggest that magma is coming directly from the mantle—passing rapidly through the crust.”
Study lead author Charlotte DeVitre, now a postdoctoral fellow at the University of California, Berkeley, said in the statement that “at Fogo volcano, magma must be driven up rapidly by the carbon dioxide and this likely plays a significant role in its explosive behavior.” Magman has extremely low viscosity, she noted.
The discovery could help mitigate the danger posed by these outbreaks. “Because deep magma storage will not be detected by ground deformation until the melt is close [the] surface, this has important implications for our understanding of volcanic hazards,” Gazel said. “With precise measurements that tell us where eruptions start, where magma melts and where it’s stored — and what triggers the eruption — we can develop a much better plan for future outbreaks.”
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