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Extinct offshore volcano could store gigatons of carbon dioxide
By Laura Fattaruso
May 23, 2023
![](images/images_05_31_2023/pic2.jpg)
Annotated seismic cross-section of the Fontanelas
volcano. Credit: Pereira and Gamboa, 2023
A new study published in Geology concludes that
an extinct volcano off the shore of Portugal could store as much as
1.2–8.6 gigatons of carbon dioxide, the equivalent of ~24–125 years of
the country's industrial emissions.
For context, in 2022 a total of 42.6 megatons (0.0426 gigatons) of
carbon dioxide was removed from the atmosphere by international carbon
capture and storage efforts, according to the Global CCS Institute.
The new study suggests that carbon capture and storage in offshore
underwater volcanoes could be a promising new direction for removal
and storage of much larger volumes of the greenhouse gas from the
atmosphere.
"We know that most countries, including Portugal, are making efforts
to decarbonize the economy and our human activities, this is a message
that this may be one of the instruments to solve the problem" says
Ricardo Pereira, a geologist at the NOVA School of Science and
Technology, and co-author of the study.
Storing carbon dioxide in an extinct volcano would rely on a process
known as "in situ mineral carbonation." In this process, carbon
dioxide reacts with elements in certain types of rocks to produce new
minerals that safely and permanently store the carbon dioxide.
Elements like calcium, magnesium, and iron combine with carbon dioxide
to form the minerals calcite, dolomite, and magnesite, respectively.
Rocks that contain large amounts of calcium, iron, and magnesium are
ideal candidates for this process—such as the volcanic basalts that
make up most of the sea floor. Knowing this, the researchers targeted
an offshore volcano for a few reasons—the structure of the volcano
could provide an ideal architecture for carbon injection and storage,
the rocks are the right type for the reactions involved, and the
location Is not too close to large populations, but also not too far.
Most carbon capture projects have relied on injection of carbon
dioxide into porous sedimentary basins that are sealed to prevent
migration of the gas out of reservoirs. In these cases, the carbon
will eventually start to form minerals, but only over longer periods
of time—decades to centuries. In 2016, researchers published findings
that 95% of carbon dioxide injected into underground basalts in
Iceland had mineralized within just two years. The much shorter
mineralization time makes the process safer and more effective—once
carbon is stored in minerals, issues like potential leaks are no
longer a concern.
Davide Gamboa, a geologist at the University of Aveiro and co-author
of the study, explains, "What makes mineral carbonation really
interesting is the time. The faster it gets into a mineral, the safer
it becomes, and once it's a mineral, it is permanent."
![](images/images_05_31_2023/pic3.jpg)
Schematic cross-section of the Fontanelas volcano, indicating possible
sites for carbon dioxide sequestration.
The researchers studied the storage potential at the ancient
Fontanelas volcano, which is partially buried ~100 kilometers offshore
from Lisbon, with a peak ~1500 meters below sea-level.
To estimate the potential volume of carbon dioxide that could be
stored at this site, the authors used 2D and 3D seismic studies of the
undersea volcano that had been produced during offshore
oil exploration, as well as data from samples that had been
dredged from the area in 2008. The dredged samples contained naturally
formed carbonate minerals, indicating that the chemical
reactions required to store carbon were already happening, and
that intentional efforts to mineralize carbon in these rocks should be
successful.
The samples also had up to 40% pore space—meaning there are spaces
within the rocks where carbon dioxide could be injected and
mineralized. The researchers also indicate that low-permeability
layers imaged around the flanks of the volcano could help with
containing the carbon dioxide before it is mineralized.
While this study demonstrated a large potential carbon storage
capacity at the Fontanelas volcano, the authors highlight that many
other places around the world may have similar offshore volcanoes that
could be candidates for carbon capture and storage.
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