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THE HRAUN PROJECT: NEW VOLCANIC CAVES ON THE REYKJANES PENINSULA Tommaso Santagata As speleologists, we are accustomed to exploring ancient caves even if they were formed thousands or even millions of years ago, in the wake of long geological, physical and chemical processes that today allow us to make our way inside them to document them and study their history. We often try to imagine what was their prior to their formation, pondering what the landscape looked like before those processes began to excavate their way through a mountain, eventually creating a link between the outside world and the unknown, but it is not always easy to interpret these processes, which for the most part occurred before we human beings even appeared on this planet. Over the average lifespan of a human, it is very unlikely that anyone could visit a landscape before and after the formation of a cave – but “very unlikely” is not the same as “impossible”. Volcanic caves are perhaps the only cavities that afford us this possibility. Naturally, glacier mills and contact caves that are located near to and inside glaciers have a genesis that is very rapid, but we are well aware of the fact that the processes leading to their formation are markedly different with respect to those for caves made of rock. In addition, in most cases, the caves in question also have a very short lifespan, closely bound up with that of the glacier and the external climatic conditions. In contrast to glacier caves, volcanic caves develop following eruption events that drastically and permanently modify the landscape both externally and in the subsoil, and as such they can have a far longer duration. Speleologists are far more likely to find themselves exploring volcanic caves that have long ago completed their process of formation, entering them once the lava has solidified. We are talking about hundreds, thousands or millions of years after they have cooled.
In rare cases, speleologists may find themselves investigating caves that formed just a few years before. When this has happened, it has been possible to document hitherto unknown minerals, defined as “metastable”, meaning that they are only found in certain chemical and physical conditions, before they have reached their state of stability. The project Last year, we had the opportunity to start work on a new project concerning the study of new volcanic caves formed recently following the eruption of the Fagradasfjall volcano on the Reykjanes peninsula in the Suðurland region. This event was preceded by intense seismic activity and by the rapid rising of the ground near a mountain close to the volcano – Mount Þorbjörn. After approximately eight hundred years of dormancy, for around six months starting from the night of 19 March 2021, this volcano erupted continuously, providing a unique spectacle, with explosions and lava fountains up to 500 metres in height. Lateral fractures on the volcano emitted around 150 million m3 of lava, forming a lava field stretching for almost 5 km2. During the eruption, we could observe how the lava tubes constitute major flow routes that contribute to the sliding of the lava, down into the subsoil and elsewhere. From the speleological perspective, this phenomenon immediately attracted the attention of geologists and researchers in our association. The event was monitored by means of various webcams installed near the volcano by the island authorities, and a plethora of amateur videos were posted on the internet, fostering the idea to undertake a study of the possible formation of new volcanic caves created as a result of the eruption.
