Earthquakes may generate huge volumes of hydrogen within the planet by fracturing rocks that then react with water molecules. This hydrogen could be an overlooked source of energy for life deep underground, as well as for people aiming to extract the gas as an alternative fuel.
The past few years have seen an explosion of interest in finding large deposits of hydrogen gas underground to use as a clean-burning fuel. For the most part, companies searching for these deposits have focused on “geologic hydrogen” generated by water that either reacts with iron-rich rock – a process called serpentinisation – or is split by radioactive minerals.
at Grenoble Alpes University in France and his colleagues became curious about other mechanisms of generating the gas after they measured high concentrations of hydrogen in soil samples from the Pyrenees. They couldn’t explain its source. One possible hydrogen-generating mechanism was silicate minerals crushed by earthquakes. “When you break the silicate-oxygen bond, you will produce a highly reactive [quartz surface] that can interact with water to produce hydrogen and a free radical,” says Lefeuvre. The reaction happens in just seconds after the rock is fractured.
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Other researchers have previously that this “mechanoradical” reaction could generate hydrogen, and hydrogen has been measured in soils above a number of active faults. But no one had calculated the total amount of hydrogen that might be generated this way.
To get a better estimate, Lefeuvre and his colleagues used a ball milling machine, a device used to break down rocks, to crush pieces of quartz of varying silica content in water. They then measured the amount of hydrogen that was produced. By changing the speed of the ball mill, they could simulate how the quartz would fracture during earthquakes of different magnitudes.
Based on these measurements, they estimated that in any given year, earthquakes over magnitude 4 cumulatively produce as much as 29 million tonnes of free hydrogen gas. That is a maximum estimate, and relies on a few big assumptions, such as that every fault is entirely covered in quartz. But it suggests earthquake hydrogen may be just as large a source of the gas as the other water-rock reactions, and that faults could be a good place to search for hydrogen deposits, says Lefeuvre.
“Perhaps part of this hydrogen will be trapped in the fault plane,” he says. “In some cases, you can also find a kind of rock called evaporite that’s a very good seal for hydrogen.” The team’s next step is to test hydrogen production from rocks made up of different combinations of minerals, says Lefeuvre.
at the US Geological Survey, who recently of where geologic hydrogen deposits are most likely to occur in the US, says this is the “most rigorous” study of mechanoradical hydrogen he has seen. However, he’s sceptical that faults are likely to form deposits of hydrogen. “By definition, you have a lot of fluid moving in these places,” he says. “It’s going to be difficult to trap much generated hydrogen in these settings.”
Whether or not humans find a way to harvest this earthquake hydrogen, deep-living microbial life could already be using it as an energy source, says Lefeuvre. They might be “fed by hydrogen produced during an earthquake”.
Earth and Planetary Science Letters
