New findings show extinct offshore volcanoes could boost carbon storage
Since climate change has become a central priority, efforts have expanded beyond reducing greenhouse gas emissions to capturing CO2 already in the atmosphere and finding durable storage options. Reforestation, enhancing oceanic carbon uptake, and new technologies to remove CO2 are all part of this multifaceted approach. Now researchers suggest another possibility. Volcanic activity in the deep sea could help reverse some of the damage by locking away carbon in solid minerals.
This perspective is outlined in a study published in Geology, which concludes that an extinct submarine volcano off Portugal’s coast can store between 1.2 and 8.6 gigatons of carbon dioxide in basalt rock. That range is comparable to the annual emissions of a large European country binding over certain decades, illustrating significant storage potential.
According to the authors, the finding adds a practical tool to decarbonization strategies. Ricardo Pereira, a geologist at the NOVA School of Science and Technology and a co-author of the paper, notes that many countries are intensifying efforts to lower carbon footprints, and mineral carbonation in volcanic rock could become part of the solution.
There are many submarine volcanoes around the world that might be suitable for this approach, according to the study. Furthermore, data from the CCS Global Institute indicate that 2022 saw around 42.6 megatons of atmospheric CO2 removed through various methods, suggesting that a single volcano could surpass the cumulative achievement of recent years by a substantial margin.
CO2 stored in rocks
The process described is mineral carbonation, which occurs on site when CO2 reacts with minerals such as calcium, magnesium, or iron to form stable carbonates like calcite, dolomite, and magnesite. This chemistry enables long term carbon storage in solid minerals, rather than in fluid reservoirs.
Basalt rocks are particularly promising for this chemistry because they contain abundant of these reactive minerals. After identifying Fontanelas volcano off Portugal as a promising site, researchers examined several factors. Its structure could provide an ideal framework for injecting and storing carbon, the rocks contain the right minerals for the desired reactions, and its location is favorable for sustained operations without intense disruption to nearby communities.
The Fontanelas site sits roughly 100 kilometers off the Lisbon coast, with its summit about 1,500 meters below sea level. The most recent submarine volcanic activity in the region was the Tagoro eruption near El Hierro, which occurred at a depth of about 88 meters below the surface in recent history.
Historically, many carbon storage efforts have focused on injecting CO2 into porous sedimentary basins, where the gas gradually reacts to form minerals and is meant to remain contained for decades or centuries. The basalt route accelerates mineralization, reducing the time to stabilization and lowering the risk of leakage.
Geologists emphasize that the speed of mineralization matters. Faster mineral formation improves safety and effectiveness because once carbon is locked into minerals, the risk of leakage drops dramatically. Experts also highlight that rapid mineralization strengthens long term storage confidence.
To estimate the potential capacity, researchers used 2D and 3D seismic surveys conducted during offshore oil exploration in 2008, along with samples from the area. They reported up to 40 percent pore space, the fraction of rock that can be filled by injected CO2 to enable mineralization.
Despite the strong findings at Fontanelas, the study notes that many other marine volcanoes worldwide could host similar carbon capture and storage projects. The Fontanelas case is presented as a candidate model illustrating how submarine volcanism could contribute to climate mitigation efforts.
Further research is encouraged to map other marine volcanic systems and assess their mineralization potential, alongside environmental and logistical considerations necessary for safe deployment. The study underscores a growing interest in leveraging geology as part of a broader strategy to stabilize atmospheric CO2.
Researchers stress the value of integrating marine geology with carbon accounting and policy planning to ensure engagement with coastal communities, regulatory frameworks, and long term monitoring. The Fontanelas findings add to a growing body of evidence that Earth systems science can inform practical climate solutions.