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Subsea Volcanoes Could Be The Key To Reaching Net-Zero
A new study suggests offshore volcanoes can store gigatonnes of carbon dioxide indefinitely.
We are living through the carbon capture boom. Literally billions of dollars of funding are flowing into countless carbon capture technology startups, all with hopes of holding back the looming climate apocalypse. There is only one problem. Where on Earth do we store it? And how do we make sure this planet-wrecking gas stays locked away? Well, new research suggests that extinct subsea volcanoes can safely and securely hold billions of tonnes of carbon dioxide practically indefinitely. This discovery opens up the possibility of being able to stop, or even reverse, climate change through carbon capture, as there are literally thousands of these volcanoes around the world. But how can a volcano store carbon dioxide? And is this really the climate solution we have been looking for?
This study focused on a subsea volcano just off Portugal called the Fontanelas volcano. It is 100 km offshore from Lisbon, and its peak resides 1,500 km beneath the waves. The reason they chose this volcano is that a vast amount of data already exists on it, the volcano has an ideal structure for carbon storage, and the location Is just the right distance away from highly populated areas.
By using 2D and 3D seismic studies of the undersea volcano that had been produced during offshore oil exploration of the area and data from dredging of the volcano in 2008, the researchers were able to figure out in detail the structure of the volcano and what rocks it is composed of. The dredged samples contained sizeable amounts of carbonate minerals. They also found that the igneous rock the volcano is made of is 40% porous, meaning that porous holes made up 40% of its volume. Despite this porousness, they found that low-permeability layers flank the volcano, effectively sealing in anything contained within the porous inner rocks.
Using this data, they estimated that this extinct volcano can store 1.2 to 8.6 billion tonnes of carbon dioxide! How? Through in situ mineral carbonation. Allow me to explain.
Certain types of rocks can react with carbon dioxide under high pressures and temperatures, such as those found at geological hot springs or within a volcano. Rocks rich in calcium, magnesium, and iron combine with the carbon dioxide in these conditions to form carbonate minerals, such as calcite, dolomite, and magnesite. This effectively turns the carbon dioxide into a solid, stable mineral, and these minerals can last for literally millions of years without breaking down and releasing their locked-away carbon dioxide.
Now, the carbonate rocks the researchers found in the dredging samples show that this process is already naturally happing within the volcano. This means the minerals within it must be rich in calcium, magnesium, and iron. The fact the volcano is 40% porous shows that there is enough room within the volcano to pump in carbon dioxide, and access these minerals to form carbonates. What’s more, the low-permeability layers that flank the volcano will act as a seal, trapping any injected carbon dioxide long enough for it to react and form carbonate minerals. Furthermore, as the volcano is extinct, there is very little chance of these minerals degrading and releasing their carbon dioxide for a very, very long time.
This process isn’t new, and is well understood. In fact, many carbon capture companies, such as CarbFix and Climeworks, already use this method. But rather than a volcano, they pump their captured carbon dioxide into sedimentary basins that have been capped off to seal them away. These basins have far lower pressures and temperatures than the volcano, so the reaction is much slower. However, this method does work. A 2016 study found that 95% of the carbon dioxide Carbfix put into their in situ mineral carbonation basin was mineralised over a two-year period.
The problem is, there aren’t many locations like these sedimentary basins, each basin can only store a relatively small amount of carbon, and it takes too long for it to fully carbonise. Presently, this isn’t an issue, as we are only storing away 0.0426 gigatons of carbon dioxide each year. But, in order to capture the billions of tonnes of carbon dioxide we need to slow climate change, we need another storage solution that is faster, more numerous and capable of holding far more carbon dioxide. The research suggests that extinct volcanoes might be the solution.
You see, the Fontanelas volcano isn’t particularly special. Its structure and composition are quite common. But the sea floor is littered with volcanos. There are around 75,000 subsea volcanoes taller than 1 km (i.e. same size or taller than the Fontanelas volcano), and the vast majority of them are extinct. This means that globally extinct subsea volcanoes could store up to 322,500 gigatonnes of carbon dioxide!
Now, humanity is currently emitting around 36 gigatonnes of carbon dioxide each year. Which means that, in theory, using subsea volcano carbon storage, we could offset 8,958 years' worth of emissions at the current rate. But, it won’t be practical to use carbon storage in this way.
You see, scientists estimate that if we adopt low-emission technology, we only need 10 gigatonnes of carbon storage each year to reach net-zero. As such, this volcano storage can help us reach net-zero for 32,250 years!
Now, we don’t know if all of these thousands of volcanoes have the same internal structure as the Fontanelas volcano. They might be far less porous, not contain the right types of minerals, and might lack the low-permeability layers that stop the carbon dioxide from bubbling out before it has a chance to turn to rocks. So, many of them might not be suitable for carbon storage. But that is okay, as we only require a fraction of them to be to reach net-zero, and chances are there are enough volcanoes like Fontanelas out there for our needs.
But, this doesn’t mean we have a nice solution to climate change. Scaling up carbon capture to this level will be one hell of a task. Then creating the infrastructure needed to get this captured carbon into the volcanos is a whole other ball game. It will require vast pipelines, or even ocean-based carbon capture, such as Captura’s (read more here), that could float above the volcano.
The fact is that this study has opened up the possibility of carbon capture being a genuinely usable and practical way to reach net-zero. Beforehand, we didn’t know where we were going to be able to store these billions of tonnes of carbon dioxide safely for the next century or so, making carbon capture a potentially problematic climate solution. But now, we do. All we need to do, is scale carbon capture technology, and cut our emissions by 72.2% before 2050, and we are at net-zero, and the planet is saved. Both of those things are possible, we just have to do it.
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