Gas Monitoring at Volcanic Fields outside Naples Exposes Multiple Sources
of Carbon Dioxide Emissions
New Geology Geoscience from The Geological Society of America
Boulder, Colo., USA: The Phlegraean volcanic fields just west of Naples,
Italy, are among the top eight emitters of volcanic carbon dioxide in the
world. Since 2005, the Solfatara crater—one of many circular depressions in
the landscape left by a long history of eruptions—has been emitting
increased volumes of gas. Today it emits 4,000-5,000 tons of carbon dioxide
each day, equivalent to the emissions from burning ~500,000 gallons of
gasoline. In a new paper published ahead of print in Geology on
Thursday, researchers estimate that as much as 20%–40% of the current
carbon dioxide emissions are from the dissolution of calcite in the rocks,
while 60%–80% is from underground magma.
“Estimating the source of the carbon dioxide is important to properly
reconstruct what is happening in the magmatic system and the hydrothermal
system,” says Gianmarco Buono, a volcanologist at the Italian National
Institute of Geophysics and Volcanology and lead author of the study. “Our
aim is to provide a tool to better discriminate the contribution of
magmatic and non-magmatic carbon dioxide that can also be applied to other
systems.”
When magma moves toward Earth’s surface, the decreasing pressure on the
magma results in degassing—the release of gases that were previously
trapped inside the magma—including water vapor, carbon dioxide, and sulfur
dioxide. Scientists monitor volcanoes for unrest and possible eruptions
using a variety of observations—detecting earthquakes and tremors related
to magma movement, taking detailed measurements of ground deformation, and
assessing the types and volumes of gases released at the surface from
fumaroles—openings in the earth that emit steam and other gases.
Eruptions are often preceded by increased fluxes of gas, but that does not
mean that every increase in gas emissions will be followed by an eruption.
It is also possible for carbon dioxide to come from sources besides magma.
Interaction between hot underground fluids and host rocks can also release
carbon dioxide.
The Italian National Institute of Geophysics and Volcanology has been
monitoring gas emissions from Solfatara crater since 1983, providing a long
record of the changes in volume and composition of the gases released
there. By comparing ratios of nitrogen, helium, and carbon dioxide in the
emissions, researchers had previously established that the gases were
coming from deep sources of magma.
“We focused mainly on geochemical variation, especially for carbon dioxide,
helium, and nitrogen, because they are non-reactive species. They contain
information about what is happening in the magma,” explains Buono.
But when the region started experiencing increased unrest in 2005, the data
began to deviate from the chemical fingerprints of the magmas, a trend that
continued to increase over time alongside rising temperatures in the
shallow hydrothermal system. The unrest continued, and in 2012 the alert
level was raised from green to yellow, indicating that there is heightened
activity but not an imminent threat of eruption.
In addition to small earthquakes and higher gas emissions, the region also
experienced deformation of the ground surface. Circulation of hot fluids
underground could explain the rising temperatures, ground deformation, and
increased gas emissions—interaction of hot acidic fluids with calcite in
the rocks also releases carbon dioxide. Drill cores of the rocks from
previous studies reveal that calcite in the rocks has similar composition
to the gas emissions. The researchers estimate that 20%–40% of the carbon
dioxide at the Solfatara crater site was from removal of the calcite in the
host rock.
The Phlegraean Fields have hosted volcanic activity since first erupting
~40,00 years ago, with the most recent eruption in 1538. There have been
several unrest phases since the 1950s. The current research is part of a
strategic project by the Italian National Institute of Geophysics and
Volcanology,
LOVE-CF: Linking surface Observables to sub-Volcanic plumbing-system: a
multidisciplinary approach for Eruption forecasting at Campi Flegrei
caldera (Italy).
FEATURED ARTICLE
Discriminating carbon dioxide sources during volcanic unrest: The case of
Campi Flegrei caldera (Italy)
Gianmarco Buono; Stefano Caliro; Antonio Paonita; Lucia Pappalardo;
Giovanni Chiodini
Contact: Gianmarco Buono, gianmarco.buono@ingv.it
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50624.1/620796/Discriminating-carbon-dioxide-sources-during
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