Geologists have found that the search for underground hydrogen deposits could be particularly worthwhile in the Pyrenees and Central Alps. These mountains offer favorable geological conditions for geochemical reactions that produce hydrogen underground. Crucial for such H2-Reservoirs are therefore sufficient expansion of the earth’s crust before mountain formation begins and the right amount of erosion. This knowledge could now make the search for underground hydrogen deposits easier.
Hydrogen (H2) is considered an important energy source of the future, but so far the gas has to be produced chemically – for example through the electrolysis of water or methane reduction. Natural deposits underground seemed to be in short supply for a long time because hydrogen is very volatile and easily escapes from the rock. But recently, geologists in several regions have discovered evidence of larger subterranean H2-Reservoirs found.
According to a study from 2025, there could even be up to ten million megatons of natural hydrogen underground globally. “We now know that the Earth produces large amounts of hydrogen, and local-scale use is already taking place in Mali,” explains lead author Frank Zwaan from the University of Lausanne. But where are these hydrogen deposits – and where is the most promising place to search for them?
How mountain formation and hydrogen deposits are related
Zwaan and his team have now examined this in more detail. The focus of their study was mountain ranges such as the Alps, the Pyrenees and the Andalusian Fold Mountains. They were formed when tectonic plates initially drifted apart millions of years ago, then moved closer together again and collided. As a result, the ground was compressed, raised and folded into mountains. Geologists refer to this as a rift inversion mountain formation.
The interesting thing about it: During the course of such mountain formation, iron-containing mantle rocks such as olivine and orthopyroxene reach near the surface and can react with water there. Under certain circumstances, this serpentinization releases hydrogen gas, which collects under impermeable overlays and produces H2-Reservoirs can form. In an earlier study, Zwaan and his colleagues had already determined that large mountain ranges formed by rift inversion could offer favorable conditions for such a geological “hydrogen kitchen”.
Thinned and raised
Geologists have now examined in more detail which mountain ranges could contain such geological hydrogen reservoirs. To do this, they used a geophysical model in which they simulated the rift inversion mountain formation. Zwaan and his team varied both the duration of the initial rift phase and the extent of erosion during the subsequent mountain formation.
It turned out that a first important factor for hydrogen production is the duration of the initial plate expansion: if this is too short, the earth’s crust does not thin out enough. As a result, not enough mantle rock can reach the surface later during uplift and folding. “Efficient serpentinization and hydrogen production can only take place if mantle rock is brought into a favorable temperature range near the surface,” explain the geologists. The simulation showed that this mainly happens with a longer rift phase of at least 15 million years.
Erosion: It’s all about the right dose
However, a second factor is even more important: erosion. “Unexpectedly, erosion turns out to be a central and ambivalent factor in the production of natural hydrogen,” reports Zwaan. “Our simulations show that it can help bring mantle material closer to the surface.” As erosion removes the crustal rock, more mantle rock reaches the cooler temperature range in which the hydrogen-producing reactions take place.
However, it depends on the right amount of erosion. “Excessive erosion causes the mantle material to rise too quickly, thereby reducing the potential for natural hydrogen formation,” the geologists explain. The rapidly exposed mantle rock is then still too hot for efficient serpentinization. In addition, excessive removal also removes impermeable cover rocks under which the resulting hydrogen could collect. As a result, the gas escapes and no H can be produced2-Reservoir arise.
Pyrenees and Central Alps are promising
But what do these findings mean specifically? Which European mountains offer the most favorable conditions? Zwaan and his team also have initial information about this. The most promising could therefore be H2-Search be in the western part of the Pyrenees. There the rift phase was long enough to bring mantle material up, but at the same time there was only moderate erosion during mountain formation. “This means that a large part of the mantle rock is in the serpentinization window and the prerequisites for an H2enrichment are cheap,” the team writes.
The search for hydrogen in the Italian part of the Central Alps could also be worthwhile. “Mantle rocks appear on the surface there, and the crust and sediment have been removed,” report Zwaan and his colleagues. As a result, the sealing cover layers are missing in many places, but favorable temperature conditions prevail and there are faults that can drain the gas formed into suitable reservoirs. “This could provide opportunities for unconventional extraction of natural hydrogen,” say the geologists.
A mountain range with rather unfavorable conditions, on the other hand, is the Andalusian Fold Mountains. There, too, mantle rock comes to the surface and there is evidence of severe erosion. Unlike in the Alps, however, the faults through which hydrogen could get into suitable storage rocks are missing. “The new results give us a better idea of where we should investigate,” says Zwaan. “They support the assumption that the Pyrenees and the Alps are important target areas for the exploration of natural H2 are.”
Source: Frank Zwaan (University of Lausanne) et al., Journal of Geophysical Research Solid Earth, 2026; doi: 10.1029/2025JB033255